10-Q

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

(Mark One)
ý	QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
For the quarterly period ended June 30, 2015
OR
o	TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
For the Transition Period from                                  to

Commission File Number: 001-36812

FLEX PHARMA, INC.

(Exact name of Registrant as specified in its charter)

Delaware (State or Other Jurisdiction of Incorporation or Organization) 46-5087339 (I.R.S. Employer Identification Number)

800 Boylston Street, 24^th Floor, Boston, MA 02199

(Address of principal executive offices)(Zip Code)

Registrant's Telephone Number, Including Area Code: (617) 874-1821

Former Name, Former Address and Former Fiscal Year, If Changed Since Last Report: Not Applicable

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to the filing requirements for the past 90 days. Yesý Noo

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Website, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yesý Noo

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definition of "large accelerated filer," "accelerated filer" and "smaller reporting company" in Rule 12b-2 of the Exchange Act. (Check one):

Large Accelerated Filero	Accelerated Filero	Non-accelerated Filerý	Smaller Reporting Companyo
		(Do not check if a smaller reporting company)

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act.) Yeso Noý

As of July 31, 2015, there were 17,938,334 shares of common stock outstanding.

FLEX PHARMA, INC.

TABLE OF CONTENTS

		Page
PART I.	Financial Information
Item 1.	Financial Statements (Unaudited)	4
	Condensed Consolidated Balance Sheets	4
	Condensed Consolidated Statements of Operations and Comprehensive Loss	5
	Condensed Consolidated Statements of Cash Flows	6
	Notes to Condensed Consolidated Financial Statements	7
Item 2.	Management’s Discussion and Analysis of Financial Condition and Results of Operations	13
Item 3.	Quantitative and Qualitative Disclosures about Market Risk	21
Item 4.	Controls and Procedures	22
PART II.	Other Information
Item 1.	Legal Proceedings	22
Item 1A.	Risk Factors	22
Item 2.	Unregistered Sales of Equity Securities and Use of Proceeds	23
Item 3.	Defaults Upon Senior Securities	23
Item 4.	Mine Safety Disclosures	23
Item 5.	Other Information	23
Item 6.	Exhibits	24
SIGNATURES		25

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This Quarterly Report on Form 10-Q contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements related to present facts or current conditions or historical facts, contained in this Quarterly Report on Form 10-Q, including statements regarding our strategy, future operations, future financial position, projected costs, potential indications for our drug product candidates, expectations regarding the development of our drug product candidates and the launch of our consumer products, the expected timing for the reporting of data from ongoing and future studies, prospects, plans and objectives of management, are forward looking statements. The words "anticipate," "believe," "estimate," "expect," "intend," "may," "plan," "predict," "project," "target," "potential," "will," "would," "could," "should," "continue" and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words.

Forward-looking statements are not guarantees of future performance and our actual results could differ materially from the results discussed in the forward-looking statements. Factors that could cause actual results to differ materially from those in the forward-looking statements include, but are not limited to, the status, timing, costs, results and interpretation of our clinical studies; the uncertainties inherent in conducting clinical studies; results from our ongoing and planned preclinical development; expectations of our ability to make regulatory filings and obtain and maintain regulatory approvals; our ability to develop and commercialize our consumer products; anticipated positioning and attributes of our consumer products; results of early clinical studies as indicative of the results of future trials; availability of funding sufficient for our foreseeable and unforeseeable operating expenses and capital expenditure requirements; other matters that could affect the availability or commercial potential of our consumer or drug product candidates; the inherent uncertainties associated with intellectual property; and other factors discussed in this Quarterly Report on Form 10-Q, our Annual Report on Form 10-K and other filings with the Securities and Exchange Commission, or SEC.

As a result of these and other factors, we may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. We do not assume any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

PART I - FINANCIAL INFORMATION

Item 1. Financial Statements

FLEX PHARMA, INC.

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited)

	June 30, 2015			December 31, 2014
Assets
Current assets:
Cash and cash equivalents	$	106,011,672		$	33,854,153
Prepaid expenses and other current assets	810,174			370,396
Total current assets	106,821,846			34,224,549
Property and equipment, net	118,992			85,144
Deferred IPO issuance costs	—			1,074,794
Deferred tax assets	50,103			50,103
Other assets	85,200			50,000
Restricted cash	126,835			126,808
Total assets	$	107,202,976		$	35,611,398
Liabilities, convertible preferred stock and stockholders' equity (deficit)
Current liabilities:
Accounts payable	$	812,321		$	578,653
Accrued expenses and other current liabilities	1,229,351			416,524
Deferred tax liabilities	50,103			50,103
Deferred rent, current portion	21,881			21,881
Total current liabilities	2,113,656			1,067,161
Deferred rent, net of current portion	27,527			35,968
Other long term liabilities	415,442			15,442
Total liabilities	2,556,625			1,118,571
Convertible preferred stock:
Series A convertible preferred stock, $0.0001 par value; none and 16,000,000 shares authorized at June 30, 2015 and December 31, 2014, respectively, and none and 15,775,221 shares issued and outstanding at June 30, 2015 and December 31, 2014, respectively	—			15,637,032
Series B convertible preferred stock, $0.0001 par value; none and 14,500,000 shares authorized at June 30, 2015 and December 31, 2014, respectively, and none and 14,078,647 shares issued and outstanding at June 30, 2015 and December 31, 2014, respectively	—			25,394,135
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 10,000,000 shares and none authorized at June 30, 2015 and December 31, 2014, respectively; none issued or outstanding at June 30, 2015 and December 31, 2014	—			—
Common stock, $0.0001 par value; 100,000,000 and 61,000,000 shares authorized at June 30, 2015 and December 31, 2014, respectively, 17,938,334 and 5,434,301 shares issued at June 30, 2015 and December 31, 2014, respectively, and 15,190,856 and 2,215,711 shares outstanding at June 30, 2015 and December 31, 2014, respectively	1,519			221
Additional paid-in capital	125,751,671			1,472,299
Accumulated deficit	(21,106,839		)	(8,010,860		)
Total stockholders' equity (deficit)	104,646,351			(6,538,340		)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$	107,202,976		$	35,611,398

See accompanying notes to condensed consolidated financial statements.

4

FLEX PHARMA, INC.

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited)

	Three Months Ended June 30, 2015			Three Months Ended June 30, 2014			Six Months Ended June 30, 2015			Period from February 26, 2014 (Inception) to June 30, 2014
Operating expenses:
Research and development	$	3,190,178		$	1,099,644		$	5,995,124		$	1,129,667
General and administrative	3,904,403			1,092,665			7,120,615			1,155,365
Total operating expenses	7,094,581			2,192,309			13,115,739			2,285,032
Loss from operations	(7,094,581		)	(2,192,309		)	(13,115,739		)	(2,285,032		)
Interest income, net	16,183			2,658			19,760			2,658
Net loss	$	(7,078,398	)	$	(2,189,651	)	$	(13,095,979	)	$	(2,282,374	)
Comprehensive loss	$	(7,078,398	)	$	(2,189,651	)	$	(13,095,979	)	$	(2,282,374	)
Net loss per share attributable to common stockholders — basic and diluted	$	(0.47	)	$	(1.42	)	$	(1.04	)	$	(1.53	)
Weighted-average number of common shares outstanding — basic and diluted	15,034,764			1,539,463			12,620,771			1,493,403

See accompanying notes to condensed consolidated financial statements.

5

FLEX PHARMA, INC.

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited)

	Six Months Ended June 30, 2015			Period from February 26, 2014 (Inception) to June 30, 2014
Operating activities
Net loss	$	(13,095,979	)	$	(2,282,374	)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	20,714			1,981
Stock-based compensation expense	3,386,319			320,684
Other non-cash items	—			55,221
Changes in operating assets and liabilities:
Restricted cash	(27		)	(126,595		)
Prepaid expenses and other current assets	(439,778		)	(69,223		)
Other assets	(35,200		)	—
Accounts payable	558,068			399,888
Accrued expenses and other current liabilities	1,008,976			374,332
Deferred rent	(8,441		)	48,190
Other long term liabilities	—			15,442
Net cash used in operating activities	(8,605,348		)	(1,262,454		)
Investing activities
Purchases of property and equipment	(75,562		)	(34,414		)
Net cash used in investing activities	(75,562		)	(34,414		)
Financing activities
Proceeds from initial public offering, net of offering costs	80,435,430			—
Proceeds from issuance of Series A convertible preferred stock, net of issuance costs	—			15,581,811
Proceeds from sale of restricted common stock to founders	—			2,321
Proceeds from exercise of stock options	402,999			—
Net cash provided by financing activities	80,838,429			15,584,132
Net increase in cash and cash equivalents	72,157,519			14,287,264
Cash and cash equivalents at beginning of period	33,854,153			—
Cash and cash equivalents at end of period	$	106,011,672		$	14,287,264
Supplemental cash flow information
Deferred IPO issuance costs in accounts payable and accrued expenses at December 31, 2014	$	499,549		$	—
Property and equipment in accrued expenses at December 31, 2014	$	21,000		$	—
IPO issuance costs paid in cash through December 31, 2014	$	575,245		$	—
Issuance of Series A convertible preferred stock in satisfaction of accounts payable	$	—		$	55,221

See accompanying notes to condensed consolidated financial statements.

6

FLEX PHARMA, INC.

NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS (Unaudited)

1. Organization and operations

The Company

Flex Pharma, Inc. (the "Company") is a biotechnology company that was incorporated in Delaware on February 26, 2014 and has a principal place of business in Boston, Massachusetts. The Company is developing innovative and proprietary treatments for nocturnal leg cramps and spasms associated with severe neuromuscular conditions. The Company believes that the chemical neuro-stimulation of certain receptors in primary sensory neurons by our proprietary treatment reduces the repetitive firing, or hyperexcitability, of alpha-motor neurons, thereby preventing or reducing the frequency and intensity of muscle cramps and spasms.

The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, risks of failure of pre-clinical studies, clinical studies and clinical trials, the need to obtain marketing approval for its drug product candidates, the need to successfully commercialize and gain market acceptance of its drug product candidates and its consumer products, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and ability to transition from pilot-scale manufacturing to large-scale production of products.

In February 2015, the Company sold 5,491,191 shares of common stock (inclusive of 91,191 shares of common stock sold by the Company pursuant to the exercise of an overallotment option granted to the underwriters in connection with the offering) through an underwritten initial public offering ("IPO") at a price of $16.00 per share. The aggregate net proceeds received by the Company from the offering were approximately $79,900,000, after deducting underwriting discounts and commissions and offering expenses payable by the Company of approximately $8,000,000 (See Note 2).

Liquidity

The Company has incurred an accumulated deficit of $21,106,839 since inception and will require substantial additional capital to fund its research and development and the launch and growth of its consumer brand. The Company had cash and cash equivalents of $106,011,672 at June 30, 2015. The Company believes its existing cash and cash equivalents will be sufficient to allow the Company to fund its current operating plan for at least the next 12 months.

2. Summary of significant accounting policies and recent accounting pronouncements

The accompanying unaudited condensed consolidated financial statements reflect the application of certain significant accounting policies as described below and elsewhere in these notes to the condensed consolidated financial statements. As of June 30, 2015, the Company’s significant accounting policies, which are detailed in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2014 (the “2014 10-K”), have not changed.

Unaudited interim financial information

Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the 2014 10-K.

The condensed consolidated financial statements as of June 30, 2015, for the three months ended June 30, 2015 and 2014, for the six months ended June 30, 2015, and for the period from February 26, 2014 (inception) through June 30, 2014, and the related information contained within the notes to the condensed consolidated financial statements, are unaudited. The unaudited condensed consolidated financial statements have been prepared on the same basis as annual audited consolidated financial statements, and in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s condensed consolidated financial position as of June 30, 2015, the condensed consolidated statements of operations and comprehensive loss for the three-and six-month periods ended June 30, 2015, the condensed

7

consolidated statement of cash flows for the six-month period ended June 30, 2015, the condensed consolidated statement of operations and comprehensive loss for the three-month period ended June 30, 2014, and the condensed consolidated statements of operations and comprehensive loss and cash flows for the period from February 26, 2014 (inception) to June 30, 2014. The results for the three and six months ended June 30, 2015 are not necessarily indicative of results to be expected for the year ending December 31, 2015, or any other future annual or interim periods.

Initial public offering

On February 3, 2015, the Company completed its IPO, whereby the Company sold 5,491,191 shares of its common stock (inclusive of 91,191 shares of common stock sold by the Company pursuant to the exercise of an overallotment option granted to the underwriters in connection with the IPO) at a price of $16.00 per share. The shares began trading on the Nasdaq Global Market on January 29, 2015. The aggregate net proceeds received by the Company from the IPO were approximately $79,900,000, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. Upon the closing of the IPO, all outstanding shares of convertible preferred stock converted into 6,971,108 shares of common stock. Additionally, the Company is now authorized to issue 100,000,000 shares of common stock.

Deferred IPO issuance costs, which primarily consisted of direct incremental legal and accounting fees related to the Company's IPO, were previously capitalized at December 31, 2014. Upon the closing of the IPO in February 2015, IPO issuance costs, which totaled $1,848,737, were offset against the IPO proceeds within additional paid-in capital.

Reverse stock split

On January 15, 2015, the Company effected a one-for-4.2825 reverse stock split of its issued and outstanding common stock. All share and per share amounts related to issued and outstanding common stock and stock options included in the Company's condensed consolidated financial statements and notes to the condensed consolidated financial statements have been retroactively adjusted for all periods presented to reflect this reverse stock split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in-capital. The conversion ratios of the Company's previously outstanding shares of convertible preferred stock were also adjusted to reflect the reverse stock split.

Basis of presentation and use of estimates

The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP"). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification ("ASC") and Accounting Standards Update ("ASU") of the Financial Accounting Standards Board ("FASB"). The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company's management evaluates its estimates, which include, but are not limited to, estimates related to clinical study accruals, stock-based compensation expense, and amounts of expenses during the reported period. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.

Prior to the completion of its IPO in February 2015, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company utilized various valuation methodologies in accordance with the framework of the 2004 and 2013 American Institute of Certified Public Accountants Technical Practice Aids, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology included estimates and assumptions that required the Company's judgment. These estimates and assumptions included a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company's common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or a sale of the

8

Company. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date and materially affect the financial statements.

Principles of consolidation

The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, TK Pharma, Inc., a Massachusetts securities corporation. All significant intercompany balances and transactions have been eliminated in consolidation.

Recent accounting pronouncements

In May 2014, the FASB issued ASU No. 2014-09, "Revenue from Contracts with Customers (Topic 606)". The ASU provides for a single comprehensive model for use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The accounting standard is effective for interim and annual periods beginning after December 15, 2016 with no early adoption permitted. In April 2015, the FASB proposed a one year deferral of the effective date of this accounting update to annual periods beginning after December 15, 2017, along with an option to permit early adoption. The Company is required to adopt the amendments in the ASU using one of two acceptable methods: retrospectively to all prior reporting periods presented, with certain practical expedients permitted; or retrospectively with the cumulative effect of initially adopting the ASU recognized at the date of initial application. The Company is currently in the process of evaluating the impact of the guidance related to the Company's anticipated launch of its consumer product in the first half of 2016.

In June 2014, the FASB issued ASU No. 2014-10 "Development Stage Entities (Topic 915): Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation". Under this ASU, the definition of a development stage entity was removed from the ASC, thereby removing the financial reporting distinction between development stage entities and other reporting entities under GAAP. This standard is effective for annual reporting periods beginning after December 15, 2014. Early adoption is permitted for certain entities. The Company was eligible for early adoption and adopted this standard in the accompanying financial statements.

In August 2014, the FASB issued ASU No. 2014-15 "Presentation of Financial Statements - Going Concern (Subtopic 205-40)". The ASU requires all entities to evaluate for the existence of conditions or events that raise substantial doubt about the entity's ability to continue as a going concern within one year after the issuance date of the financial statements. The accounting standard is effective for interim and annual periods ending after December 15, 2016, and will not have a material impact on the consolidated financial statements, but may impact the Company's footnote disclosures.

In February 2015, the FASB issued ASU No. 2015-02 "Consolidation (Topic 810): Amendments to the Consolidation Analysis." ASU 2015-02 changes the analysis that a reporting entity must perform to determine whether it should consolidate certain types of legal entities. It is effective for annual reporting periods, and interim periods within those years, beginning after December 15, 2015. Early adoption is permitted, including adoption in an interim period. The Company is currently in the process of evaluating the impact of the adoption of ASU 2015-02 on its consolidated financial statements.

The Company believes that the impact of other recently issued standards that are not yet effective will not have a material effect on its consolidated financial position or results of operations upon adoption.

3. Cash equivalents

Management determines the appropriate classification of marketable securities at the time they are acquired and evaluates the appropriateness of such classifications at each balance sheet date. The Company classifies its marketable securities as available-for-sale pursuant to ASC 320, Investments - Debt and Equity Securities. Marketable securities are recorded at fair value, with unrealized gains and losses included as a component of accumulated other comprehensive income (loss) in the consolidated statement of convertible preferred stock and stockholders’ equity (deficit) and a component of total comprehensive loss in the consolidated statements of

9

operations and comprehensive loss, until realized. Realized gains and losses are included in the consolidated statement of operations and comprehensive loss as part of interest income, net, on a specific-identification basis.

The Company reviews marketable securities for other-than-temporary impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable within a reasonable period of time. Other-than-temporary impairments of investments are recognized in the consolidated statement of operations if the Company has experienced a credit loss, has the intent to sell the marketable security, or if it is more likely than not that the Company will be required to sell the marketable security before recovery of the amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and the duration of the impairment and changes in value subsequent to the end of the period.

Investments classified as current have maturities of less than one year. Investments classified as non-current are those that (i) have a maturity greater than one year and (ii) management does not intend to liquidate within the next year, although these funds are available for use and therefore classified as available-for-sale.

The Company considers all highly liquid investments with maturities of three months or less when purchased to be cash equivalents. During the second quarter of 2015, the Company purchased corporate debt securities in the form of commercial paper and senior corporate notes, all of which were originally classified as cash equivalents and matured prior to June 30, 2015. Cash equivalents as of June 30, 2015 consisted of money market funds, and the Company did not have cash equivalents as of December 31, 2014.

There were no unrealized gains or losses during the three or six months ended June 30, 2015, the three months ended June 30, 2014, or during the period from February 26, 2014 (inception) to June 30, 2014. Realized gains recognized during the three and six months ended June 30, 2015 were immaterial and no realized gains or losses were recognized during 2014.

4. Net loss per share

Basic net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period, determined using the treasury stock method and the if-converted method, for convertible securities, if inclusion of these is dilutive.

Because the Company has reported a net loss for the periods presented, diluted net loss per common share is the same as basic net loss per common share.

The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding for the periods indicated, because including them would have had an anti-dilutive impact:

	As of June 30,
	2015	2014
Unvested restricted common stock sold to founders	2,710,414	3,726,766
Unvested restricted common stock issued upon early exercise of stock options	37,064	—
Options to purchase common stock	1,363,994	297,746
Series A preferred stock	—	15,775,221
Total	4,111,472	19,799,733

10

5. Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:

	June 30, 2015		December 31, 2014
Payroll and employee-related costs	$	675,598	$	34,218
Research and development costs	275,764		125,067
Professional fees	153,584		15,500
Consumer brand-related costs	77,149		23,635
Other	47,256		42,955
Deferred IPO issuance costs	—		175,149
Total	$	1,229,351	$	416,524

6. Common stock

As of June 30, 2015, the Company had authorized 100,000,000 shares of common stock, $0.0001 par value per share. Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors.

Restricted common stock

In March 2014, the Company sold 4,553,415 shares of restricted common stock to the founders of the Company ("recipients"), for $0.0004 per share, for total proceeds of $1,950. In April 2014, based upon anti-dilution provisions granted to the recipients, an additional 867,314 shares of restricted common stock were sold to the same recipients, after which the anti-dilution provisions were terminated. The restricted common stock vested 25% upon issuance, and the remaining 75% vests ratably over four years, during which time the Company has the right to repurchase the unvested shares held by a recipient if the relationship between such recipient and the Company ceases. If the relationship terminates, the Company has 90 days to repurchase unvested shares at $0.0004 per share. Such shares are not accounted for as outstanding until they vest. As of June 30, 2015, 2,710,315 shares of restricted common stock had vested and are accounted for as outstanding common stock. Unvested restricted common stock awards to non-employees are re-measured at each vest date and each financial reporting date.

The following is a summary of restricted common stock activity related to shares sold to the Company's founders:

	Number of Shares		Weighted-Average Grant Date Fair Value
Non-vested at December 31, 2014	3,218,590		$	0.10
Vested	(508,176	)	0.10
Non-vested at June 30, 2015	2,710,414		$	0.10

Early exercise of stock options

During the first quarter of 2015, 37,064 employee stock options, with a weighted-average grant date fair value of $10.79 per share, were exercised pursuant to an early exercise provision in an employee's stock option agreement. None of the exercised options had vested as of June 30, 2015, and the early exercise provision contains a repurchase option by the Company. Accordingly, the $400,000 of exercise proceeds received by the Company are being accounted for as a liability on the Company's condensed consolidated balance sheet at June 30, 2015. The

11

proceeds received will remain classified as a liability and the related shares will not be considered outstanding, for accounting purposes, until the shares vest in the fourth quarter of 2015.

7. Stock-based compensation

In March 2014, the Company adopted the Flex Pharma, Inc. 2014 Equity Incentive Plan (the "2014 Plan"), under which it had the ability to grant incentive stock options, non-qualified stock options, restricted stock awards, restricted stock units and stock appreciation rights to purchase up to 116,754 shares of common stock. In April 2014, the Company amended the 2014 Plan to reserve for the issuance of up to 1,451,087 shares of common stock pursuant to equity awards. In September 2014, the Company further amended the 2014 Plan to reserve for the issuance of up to 2,070,200 shares of common stock pursuant to equity awards. Terms of stock award agreements, including vesting requirements, were determined by the board of directors, subject to the provisions of the 2014 Plan. For options granted under the 2014 Plan, the exercise price equaled the fair market value of the common stock as determined by the board of directors on the date of grant. No further awards will be granted under the 2014 Plan.

In January 2015, the Company's board of directors adopted, and the Company's stockholders approved, the 2015 Equity Incentive Plan (the "2015 Plan"), which became effective immediately prior to the closing of the Company's IPO. The 2015 Plan provides for the grant of incentive stock options ("ISOs"), nonstatutory stock options, restricted stock awards, restricted stock units, stock appreciation rights, performance-based stock awards, and other stock-based awards. Additionally, the 2015 Plan provides for the grant of performance-based cash awards. ISOs may be granted only to the Company's employees. All other awards may be granted to the Company's employees, including officers, and to non-employee directors and consultants. As of June 30, 2015, there were 673,080 shares remaining available for the grant of stock awards under the 2015 Plan.

The Company has awarded stock options to its employees, directors, advisors and consultants, pursuant to the plans described above. Stock options subsequent to the completion of the Company's IPO are granted with an exercise price equal to the closing market price of the Company's common stock on the date of grant. Stock options generally vest over one to four years and have a contractual term of ten years. Stock options are valued using the Black-Scholes option pricing model and compensation cost is recognized based on the resulting value over the service period. Unvested awards to non-employees are re-measured at each vest date and at each financial reporting date. The following table summarizes stock option activity for employees and non-employees for the six months ended June 30, 2015:

	Shares		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2014	926,832		$	3.40
Granted	505,748		15.02
Exercised	(41,734	)	9.65
Cancelled or forfeited	(26,852	)	9.48
Outstanding at June 30, 2015	1,363,994		$	7.40	9.37	$	13,527,657
Exercisable at June 30, 2015	98,024		$	1.51	8.93	$	1,538,006
Vested or expected to vest at June 30, 2015	1,327,695		$	7.38	9.37	$	13,189,776

12

Total stock-based compensation expense recognized for employee and non-employee restricted common stock, and stock options granted to employees and non-employees is included in the Company's condensed consolidated statement of operations and comprehensive loss as follows:

	Three Months Ended June 30, 2015		Three Months Ended June 30, 2014		Six Months Ended June 30, 2015		Period from February 26, 2014 (Inception) to June 30, 2014
Research and development	$	855,083	$	95,493	$	1,812,293	$	102,051
General and administrative	785,476		213,256		1,574,026		218,633
Total	$	1,640,559	$	308,749	$	3,386,319	$	320,684

As of June 30, 2015, there was approximately $20,334,155 of total unrecognized compensation cost related to non-vested equity awards. Total unrecognized compensation cost will be adjusted for the re-measurement of non-employee awards as well as future changes in employee and non-employee forfeitures, if any. The Company expects to recognize that cost over a remaining weighted-average period of 2.87 years.

Employee stock purchase plan

In January 2015, the Company's board of directors adopted, and the Company's stockholders approved, the 2015 Employee Stock Purchase Plan (the "ESPP"), which became effective upon the date of execution of the underwriting agreement pursuant to which the Company's common stock was priced in connection with the IPO. As of June 30, 2015, the Company had not yet instituted any offering periods under the ESPP and no shares of the Company's common stock have been purchased under the ESPP.

8. Income taxes

Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Based upon the Company's history of operating losses and the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets. There was no significant income tax provision or benefit for the three or six months ended June 30, 2015, for the three months ended June 30, 2014 or for the period from February 26, 2014 (inception) to June 30, 2014.

Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations

The following discussion and analysis should be read in conjunction with the unaudited financial information and the notes thereto included herein, as well as our audited consolidated financial statements and notes thereto contained in our Annual Report on Form 10-K for the year ended December 31, 2014. Our actual results and the timing of selected events could differ materially from those anticipated in these forward-looking statements as a result of several factors, including those set forth under "Risk Factors" discussed in our Annual Report on Form 10-K for the year ended December 31, 2014.

Introduction

Our Management's Discussion and Analysis of Financial Condition and Results of Operations (MD&A) is provided in addition to the accompanying condensed consolidated financial statements and notes to assist readers in understanding our results of operations, financial condition, and cash flows. MD&A is organized as follows:

13

Overview - A discussion of our business and overall analysis of financial and other highlights affecting the company in order to provide context for the remainder of MD&A.

Results of Operations - An analysis of our financial results comparing the three months ended June 30, 2015 to the three months ended June 30, 2014, and comparing the six months ended June 30, 2015 to the period from February 26, 2014 (inception) to June 30, 2014.

Liquidity and Capital Resources - An analysis of changes in our condensed consolidated balance sheets and cash flows, and discussion of our financial condition and potential sources of liquidity.

Critical Accounting Policies and Significant Judgments and Estimates - A discussion of critical accounting policies that require us to make subjective estimates and judgments.

Overview

We are a biotechnology company that is developing innovative and proprietary treatments for exercise-associated muscle cramps, nocturnal leg cramps and spasms associated with severe neuromuscular conditions. Our founders' novel insights regarding neuromuscular physiology form the basis of our development efforts. We believe that the chemical neuro-stimulation of certain receptors in primary sensory neurons by our proprietary treatment reduces the repetitive firing, or hyperexcitability, of alpha-motor neurons, thereby preventing or reducing the frequency and intensity of muscle cramps and spasms. We also believe that we are the only company developing products based on this mechanism of muscle cramp inhibition. We have conducted three randomized, blinded, placebo-controlled cross-over studies of our proprietary treatment, which have shown a statistically significant reduction in the intensity of muscle cramps induced in healthy normal volunteers. We intend to initially focus our drug development efforts on developing a product to treat nocturnal leg cramps. There is no drug product currently available in the United States that has been approved to treat nocturnal leg cramps. We estimate, based on independent third-party survey results, that approximately four million U.S. adults over the age of 65 suffer from nocturnal leg cramps on a daily basis. We are also evaluating other indications to initially pursue, including muscle cramping associated motor neuron disease, such as amyotrophic lateral sclerosis (ALS), and spasticity associated with multiple sclerosis.

We are also developing a consumer brand with products based on the same mechanism of action as our proprietary treatment. Our consumer brand and products will be targeted towards athletes experiencing exercise-associated muscle cramps, or EAMCs. EAMCs are painful, spasmodic and involuntary contractions of skeletal muscles that occur during or following exercise in individuals with no underlying metabolic, neurological or endocrine pathology. EAMCs can be experienced by individuals participating in any sport but are particularly prevalent in athletes engaging in high-intensity activities, such as running, cycling and triathlons. There are a number of well-known sports drinks and other consumer products used to prevent EAMCs. However, we do not believe any of these products have been proven to be clinically effective in preventing EAMCs. We anticipate launching our cornerstone product in the first half of 2016.

We have incurred an operating loss since our inception and we anticipate that we will continue to incur operating losses for at least the next several years. Our net loss was $7.1 million for the three months ended June 30, 2015 and $13.1 million for the six months ended June 30, 2015. Our accumulated deficit was $21.1 million as of June 30, 2015. To date, we have financed our operations with net proceeds from the private placement of our preferred stock and our initial public offering.

Recent Developments

On January 15, 2015, we effected a one-for-4.2825 reverse stock split of our issued and outstanding common stock. All share and per share amounts related to issued and outstanding common stock and stock options included in our condensed consolidated financial statements and notes to condensed consolidated financial statements have been retroactively adjusted for all periods presented to reflect this reverse stock split. The conversion ratios of our previously outstanding shares of convertible preferred stock were also adjusted to reflect the reverse stock split.

In February 2015, we completed our initial public offering, or IPO, whereby we sold 5,491,191 shares of our common stock (inclusive of 91,191 shares of common stock sold by us pursuant to the exercise of an overallotment option granted to the underwriters in connection with the IPO) at a price of $16.00 per share. The shares began trading on the Nasdaq Global Market on January 29, 2015. The aggregate net proceeds received by us from the IPO were approximately $79.9 million, after deducting underwriting discounts and commissions and other offering expenses payable by us. Upon the closing of the IPO, all outstanding shares of convertible preferred stock were converted into 6,971,108 shares of common stock.

14

In April 2015, we initiated a human proof-of-concept efficacy study in nocturnal leg cramps with our proprietary treatment. The randomized, blinded, placebo-controlled, cross-over study is expected to enroll at least 40 subjects who experience nocturnal leg cramps at least four nights per week. This proof-of-concept study is being conducted in accordance with the regulatory framework applicable to dietary supplements rather than drugs because the U.S. Food and Drug Administration has indicated that the treatment of nocturnal leg cramps is an appropriate drug or dietary supplement claim. We are currently evaluating an additional nocturnal leg cramp study outside of the United States, expect to initiate a multiple sclerosis spasticity study in the latter half of 2015, and are evaluating a study in ALS.

In July 2015, we announced the results of a study of our proprietary treatment in athletes participating in high intensity sports. This study evaluated our proprietary treatment in a total of 23 healthy athletes who frequently suffer from muscle cramps while engaging in high intensity sports. Participants included men and women that train 3-4 times a week. Participants administered the treatment 15-30 minutes prior to exercise. The study was intended to evaluate the efficacy of our proprietary treatment in preventing muscle cramps as measured by the incidence of cramps during training sessions. The study showed statistically significant results (p<0.01 by Poisson regression), demonstrating that our treatment reduced muscle cramps during a two week workout period by more than 50% when compared to the prior two week baseline observation period. The study also demonstrated a trend towards a reduction in cramp duration. In another arm of the study, 21 healthy athletes administered our proprietary treatment as an acute treatment at the onset of a muscle cramp. These data showed positive trends with approximately two-thirds of athletes claiming relief within five minutes when our proprietary treatment was taken at the onset of a muscle cramp.

During the three months ended June 30, 2015, we also announced that Alfred Sandrock, Jr., M.D., Ph.D., and John Winkelman, M.D., Ph.D. had joined our Scientific Advisory Board. Dr. Sandrock is the Group Senior Vice President of Development Sciences and Chief Medical Officer at Biogen. Dr. Winkelman is the Chief of the Sleep Disorders Clinical Research Program at Massachusetts General Hospital and is an Associate Professor of Psychiatry at Harvard Medical School. In addition, we announced that Jeffrey D. Capello, former Chief Financial Officer of Ortho-Clinical Diagnostics, Inc., had joined our Board of Directors and would serve as Chair of the Audit Committee. In July 2015, David Julius, Ph.D. notified us that he wanted to focus primarily on his academic activities and was resigning from our Scientific Advisory Board.

During the three months ended June 30, 2015, we also announced that investors can begin following us on twitter and on our website to learn about the pre-launch activities for our consumer product to prevent and treat exercise-associated muscle cramps. Information contained on or accessible through twitter and our website is not a part of this Quarterly Report.

Components of Operating Results

Revenue

To date, we have not generated any revenue. In the future, we may generate revenue from a combination of drug product sales, consumer product sales, government or other third-party funding, marketing and distribution arrangements and other collaborations, strategic alliances and licensing arrangements, or a combination of these sources. To the extent any of our products are successfully commercialized, we expect that any revenue we generate will fluctuate from quarter to quarter as a result of the amount and timing of payments that we receive from the sale of our products, the timing and amount of license fees, milestone and other payments. If we fail to complete the development of our drug product candidates in a timely manner or obtain regulatory approval for them or fail to successfully commercialize our consumer products, our ability to generate future revenue, and our results of operations and financial position, would be materially adversely affected.

Research and Development Expenses

Our research and development expenses have related primarily to the development of our proprietary treatment for muscle cramps and spasms. These costs include salaries and other compensation-related costs, including stock-based compensation, for research and development employees, costs of clinical studies of our proprietary treatment and related research, costs for consultants who we utilize to supplement our personnel, fees paid to third parties, insurance costs, facilities and office-related expenses, cost of laboratory supplies, travel and other outside expenses.

Research and development activities are central to our business model. We have advanced our clinical efforts and expect to identify our initial drug candidate, which we believe will consist of one or two highly pure, synthesized, potent activators of transient receptor potential, or TRP, cation channel receptors. Product candidates in later

15

stages of clinical development generally have higher development costs than those in earlier stages of clinical development, primarily due to the increased size and duration of later-stage clinical trials. We expect our research and development expenses to increase in the future as we increase personnel and compensation costs, increase our research efforts, conduct proof-of-concept clinical studies and perform preclinical work of our drug product candidates. It is difficult to determine, with certainty, the duration and completion costs of our current or future pre-clinical programs, clinical studies and clinical trials of our drug product candidates.

In addition, the probability of success for each drug product candidate will depend on numerous factors, including competition, manufacturing capability and commercial viability. We will determine which programs to pursue and how much to fund each program in response to the scientific and clinical success of our proprietary treatment and each drug product candidate, as well as an assessment of each drug product candidate's commercial potential.

Research and development expenses also include costs incurred related to our consumer product, including athlete based efficacy studies of our proprietary treatment, product formulation work, stability studies and other efforts. We expect these costs to increase as we continue to test product efficacy and formulation in the consumer setting, as well as develop future consumer products.

General and Administrative Expenses

General and administrative expenses consist primarily of salaries and other compensation-related costs, including stock-based compensation, for personnel in executive, finance and accounting, legal, corporate communications and general administration roles. Other significant costs include professional service fees including legal fees relating to patent and corporate matters, accounting fees, insurance costs, costs for consultants who we utilize to supplement our personnel, travel costs, and facility and office-related costs not otherwise included in research and development expenses.

General and administrative expenses also include costs related to our consumer brand and cornerstone product. Through June 30, 2015, these costs have included personnel costs, brand development costs, market research costs, product design costs, pre-launch activity costs and other external costs. We are preparing to launch our cornerstone consumer product in the first half of 2016 and expect to initially target the following select geographic markets: Los Angeles, California, Boulder, Colorado and Boston, Massachusetts. We began pre-launch activities in the second quarter of 2015 which have included, among other things, providing product samples, gathering feedback, educating and beginning to build demand for our consumer product among our targeted demographic. We are also discussing potential relationships with professional athletes and teams. As we prepare to launch our cornerstone consumer product in the first half of 2016, costs will increase as we hire additional personnel to support our pre-launch and launch activities and incur costs related to branding, product design, packaging, distribution, and other related sales and promotion activities.

We anticipate that our general and administrative expenses will increase in the future to support our continued research and development activities and potential commercialization of our consumer products and drug product candidates and the increased costs of operating as a public company. Increases will likely include increased costs related to the hiring of additional personnel and fees to outside consultants, lawyers and accountants, among other expenses. We expect to incur additional costs associated with being a public company, including expenses related to services associated with maintaining compliance with Nasdaq listing rules and SEC requirements, insurance and investor relations costs.

Interest Income, Net

Interest income, net primarily consists of interest income from our cash and cash equivalents, amortization of bond premiums and realized gains and losses.

16

Results of Operations

Three Months Ended June 30, 2015 Compared to the Three Months Ended June 30, 2014

The following table sets forth the results of operations for the three months ended June 30, 2015 compared to the three months ended June 30, 2014. During the three months ended June 30, 2014, we were initiating operations, had a minimal workforce and had not yet commenced consumer operations.

	Three Months Ended June 30, 2015			Three Months Ended June 30, 2014			Increase (Decrease)
Operating expenses:
Research and development	$	3,190,178		$	1,099,644		$	2,090,534
General and administrative	3,904,403			1,092,665			2,811,738
Total operating expenses	7,094,581			2,192,309			4,902,272
Loss from operations	(7,094,581		)	(2,192,309		)	(4,902,272		)
Interest income, net	16,183			2,658			13,525
Net loss	$	(7,078,398	)	$	(2,189,651	)	$	(4,888,747	)

Research and Development Expenses

Research and development expenses were $3.2 million for the three months ended June 30, 2015 compared to $1.1 million for the three months ended June 30, 2014. The increase of $2.1 million was primarily related to:

• $1.2 million of personnel related costs including salaries and other compensation-related costs, including stock-based compensation, due to an increased workforce;

• $0.7 million of costs related to increased clinical studies of our proprietary treatment and related research activities;

• $0.1 million of external consulting costs incurred to supplement our research and development personnel as research, clinical and development activity increased; and

• $0.1 million of other costs, including costs related to allocated insurance, facility and office-related expenses and employee travel-related costs, primarily due to an increased workforce and activity.

General and Administrative Expenses

General and administrative expenses were $3.9 million for the three months ended June 30, 2015 compared to $1.1 million for the three months ended June 30, 2014. The increase of $2.8 million was primarily related to:

• $1.2 million of personnel costs including salaries and other compensation-related costs, including stock-based compensation, due to an increased workforce;

• $1.0 million of external costs related to developing our consumer brand and cornerstone product, including brand development, market research, product design and pre-launch costs;

• $0.2 million of professional service fees, including corporate legal costs, insurance, accounting fees, investor relations and business development expenses, as well as intellectual property legal and filing costs. These costs increased primarily as a result of being a publicly traded company;

• $0.2 million of recruiting costs and employee-related travel costs, due to increased activity and an increased workforce; and

• $0.2 million of external consulting costs incurred to supplement our increased general and administrative personnel and activities.

17

Six Months Ended June 30, 2015 Compared to the Period from February 26, 2014 (Inception) to June 30, 2014

The following table sets forth the results of operations for the six months ended June 30, 2015 compared to the period from February 26, 2014 (inception) to June 30, 2014. During the period from February 26, 2014 (inception) to June 30, 2014, we were initiating operations, had a minimal workforce and had not yet commenced consumer operations.

	Six Months Ended June 30, 2015			Period from February 26, 2014 (Inception) to June 30, 2014			Increase (Decrease)
Operating expenses:
Research and development	$	5,995,124		$	1,129,667		$	4,865,457
General and administrative	7,120,615			1,155,365			5,965,250
Total operating expenses	13,115,739			2,285,032			10,830,707
Loss from operations	(13,115,739		)	(2,285,032		)	(10,830,707		)
Interest income, net	19,760			2,658			17,102
Net loss	$	(13,095,979	)	$	(2,282,374	)	$	(10,813,605	)

Research and Development Expenses

Research and development expenses were $6.0 million for the six months ended June 30, 2015 compared to $1.1 million for the period from February 26, 2014 (inception) to June 30, 2014. The increase of $4.9 million was primarily related to:

• $2.6 million of personnel related costs including salaries and other compensation-related costs, including stock-based compensation, due to an increased workforce;

• $1.6 million of costs related to increased clinical studies of our proprietary treatment and related research activities;

• $0.4 million of external consulting costs incurred to supplement our research and development personnel as research, clinical and development activity increased; and

• $0.3 million of other costs, including costs related to allocated insurance, facility and office-related expenses and employee travel-related costs as we added personnel and increased activities.

General and Administrative Expenses

General and administrative expenses were $7.1 million for the six months ended June 30, 2015 compared to $1.2 million for the period from February 26, 2014 (inception) to June 30, 2014. The increase of $6.0 million was primarily related to:

• $2.9 million of personnel costs including salaries and other compensation-related costs, including stock-based compensation, due to an increased workforce;

• $1.5 million of external costs related to developing our consumer brand and cornerstone product, including brand development, market research, product design and pre-launch costs;

• $0.6 million of professional service fees, including corporate legal costs, insurance, accounting and intellectual property legal and filing costs, primarily related to being a publicly traded company;

• $0.5 million of recruiting costs and employee-related travel costs, due to increased activity and an increased workforce;

• $0.4 million of external consulting costs incurred to supplement our general and administrative personnel due to increased activity and an increased workforce; and

18

• $0.1 million of increased other costs, including costs related to facility and office-related expenses.

Liquidity and Capital Resources

Overview

Since inception, we have incurred an operating loss and we anticipate that we will continue to incur operating losses for at least the next several years. To date, we have not generated any revenues. We expect that our research and development and general and administrative expenses will continue to increase, and we will incur significant sales and marketing expense associated with the launch and commercialization of our consumer brand and our cornerstone product. As a result, we will need additional capital to fund our operations, which we may raise through a combination of equity offerings, debt financings, other third-party funding, marketing and distribution arrangements and other collaborations, strategic alliances and licensing arrangements.

Since our inception, we have financed our operations through private placements of equity securities and our IPO, which we completed in February 2015. During 2014, we issued 15,775,221 shares of series A convertible preferred stock and received aggregate net proceeds of $15.6 million, net of issuance costs, and we issued 14,078,647 shares of series B convertible preferred stock and received aggregate net proceeds of $25.4 million, net of issuance costs. All shares of the previously issued and outstanding series A and series B convertible preferred stock converted into 6,971,108 shares of common stock upon the close of the IPO. In our IPO, we sold 5,491,191 shares of common stock (including shares sold pursuant to to the exercise of an overallotment option granted to the underwriters) that resulted in net proceeds to us of $79.9 million. As of June 30, 2015, we had $106.0 million in cash and cash equivalents, which were held in bank deposit accounts and money market funds.

Sources of Liquidity

Cash Flows

	Six Months Ended June 30, 2015			Period from February 26, 2014 (Inception) to  June 30, 2014
Net cash (used in) provided by:
Operating activities	$	(8,605,348	)	$	(1,262,454	)
Investing activities	(75,562		)	(34,414		)
Financing activities	80,838,429			15,584,132
Net increase in cash and cash equivalents	$	72,157,519		$	14,287,264

Operating Activities

The increase in cash used in operations for the six months ended June 30, 2015 compared to the period from February 26, 2014 (inception) to June 30, 2014 was primarily due to our significant increase in operations. During the period from February 26, 2014 (inception) to June 30, 2014, we were initiating operations, had minimal workforce personnel, and had not yet commenced consumer operations. For the six months ended June 30, 2015, we incurred increased costs related to our personnel, increased costs related to our research and development efforts including clinical study costs, increased costs associated with our consumer product efforts and increased costs needed to support our operations.

Investing Activities

Net cash used in investing activities for the six months ended June 30, 2015 related to the acquisition of property and equipment, primarily computers and computer equipment, and increased from the prior year due to our increased workforce and activities.

19

Financing Activities

Net cash provided by financing activities was $80.8 million during the six months ended June 30, 2015 compared to $15.6 million for the period from February 26, 2014 (inception) to June 30, 2014. During the six months ended June 30, 2015, we completed our IPO, which resulted in net proceeds of $79.9 million. During the period from February 26, 2014 (inception) to June 30, 2014, we sold shares of series A convertible preferred stock resulting in net proceeds to us of $15.6 million.

As of June 30, 2015, we had no long-term debt.

We currently have no ongoing material financial commitments, such as lines of credit or guarantees that are expected to affect our liquidity over the next five years, other than leases.

Funding Requirements

We expect that we will require additional funding to support the launch and growth of our consumer brand and products and to develop and commercialize our drug product candidates. In addition, if we receive regulatory approval for any of our drug product candidates, and if we choose not to grant rights to commercialize our drug products to partners, we expect to incur significant commercialization expenses related to product manufacturing, sales, marketing and distribution activities. We also expect to incur additional costs to support our operations as well as the costs associated with operating as a public company.

Until we can generate a sufficient amount of revenue from our products, if ever, we expect to finance future cash needs through public or private equity or debt offerings. Additional capital may not be available on reasonable terms, if at all. If we are unable to raise additional capital in sufficient amounts or on terms acceptable to us, we may have to significantly delay, scale back or discontinue the development or commercialization of one or more of our product candidates. If we raise additional funds through the issuance of additional debt or equity securities, it could result in dilution to our existing stockholders, increased fixed payment obligations and these securities may have rights senior to those of our common stock. If we incur indebtedness, we could become subject to covenants that would restrict our operations and potentially impair our competitiveness, such as limitations on our ability to incur additional debt, limitations on our ability to acquire, sell or license intellectual property rights and other operating restrictions that could adversely impact our ability to conduct our business. Any of these events could significantly harm our business, financial condition and prospects.

Our primary uses of capital are, and we expect will continue to be, compensation and related expenses, clinical costs, third-party research and development costs, legal and other regulatory expenses, marketing, promotion and manufacturing costs related to our consumer brand and products, external consulting costs and general administrative and overhead costs. Our future funding requirements will be heavily reliant upon the resources required to support our drug product candidates as well as our consumer brand and products.

Pre-Clinical Drug Product Candidates

The successful development of any drug product candidate is highly uncertain. As such, at this time, we cannot reasonably estimate or know the nature, timing and costs of the efforts that will be necessary to complete the development of our future drug product candidates. We are also unable to predict when, if ever, material net cash inflows will commence from the sale of drug product candidates. This is due to the numerous risks and uncertainties associated with developing drug products, including the uncertainty of:

• successful enrollment in, and completion of, clinical studies and trials;

• receipt of marketing approvals from applicable regulatory authorities;

• establishing arrangements with third-party manufacturers;

• obtaining and maintaining patent and trade secret protection and regulatory exclusivity; and

• launching commercial sales of our products, if and when approved, whether alone or in collaboration with others.

A change in the outcome of any of these variables with respect to the development of any of our drug product candidates would significantly change the costs and timing associated with the development of that drug product candidate.

20

As all of our drug product candidates are in the pre-clinical phase of development and the outcome of these efforts is uncertain, we cannot estimate the actual amounts necessary to successfully complete the development and commercialization of our drug product candidates.

Consumer Brand and Products

The development and launch of our consumer brand, our cornerstone product and future products is uncertain, including the timing and resources needed to support successful commercialization. Our future success depends, in large part, on our ability to implement a launch and growth strategy that establishes distribution and placement of our products and attracts consumers to our cornerstone product and future product offerings.

Our future funding requirements will be impacted by our ability to successfully launch and grow our consumer brand and products. Delays or unexpected costs related to the consumer brand and cornerstone product launch and growth plans could significantly change the costs and the timing of such costs associated with our consumer products.

Outlook

Based on our research and development plans, our consumer brand and product launch plans and our expectations of timing related to the progress of our clinical programs, we expect that our existing cash resources will enable us to fund our operating expenses and capital expenditure requirements through mid-2018. We have based this estimate on assumptions that may prove to be wrong, however, and we could use our capital resources sooner than we expect. Additionally, the process of testing drug product candidates in clinical trials is costly, as are the resources required to launch a consumer brand and products, and the timing of progress of these efforts is uncertain.

Contractual Obligations

There have been no material changes to our contractual obligations from those described in our Annual Report on Form 10-K for the year ended December 31, 2014.

Off-Balance Sheet Arrangements

We did not have during the period presented, and we do not currently have, any off-balance sheet arrangements, as defined under SEC rules.

Critical Accounting Policies and Significant Judgments and Estimates

Our management's discussion and analysis of our financial condition and results of operations is based on our condensed consolidated financial statements, which have been prepared in accordance with accounting principles generally accepted in the United States, or GAAP. The preparation of these condensed consolidated financial statements requires us to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities as of the date of the condensed consolidated balance sheet and the reported amounts of expenses during the reporting period. In accordance with GAAP, we base our estimates on historical experience and on various other assumptions that we believe are reasonable under the circumstances at the time such estimates are made. Actual results may differ materially from our estimates and judgments under different assumptions or conditions. We periodically review our estimates in light of changes in circumstances, facts and experience. The effects of material revisions in estimates are reflected in our consolidated financial statements prospectively from the date of the change in estimate.

There have been no material changes to our critical accounting policies from those described in "Management's Discussion and Analysis of Financial Condition and Results of Operations" included in our Annual Report on Form 10-K for the year ended December 31, 2014.

Item 3. Quantitative and Qualitative Disclosures about Market Risk

The market risk inherent in our financial instruments and in our financial position represents the potential loss arising from adverse changes in interest rates. As of June 30, 2015, we had cash and cash equivalents of $106.0 million. We invest our cash in a variety of financial instruments, principally money market funds and investment-grade corporate notes and commercial paper. Our primary exposure to market risk is interest rate sensitivity, which

21

is affected by changes in the general level of U.S. interest rates. Available for sale securities that we invest in are subject to interest rate risk and will fall in value if market interest rates increase. Due to the short-term duration of our investment portfolio and the low risk profile of our investments, an immediate 100 basis point change in interest rates would not have a material effect on the fair market value of our portfolio.

Item 4. Controls and Procedures

Evaluation of Disclosure Controls and Procedures

We maintain disclosure controls and procedures that are designed to ensure that information required to be disclosed in our periodic and current reports that we file under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), with the SEC is recorded, processed, summarized and reported within the time periods specified in the SEC’s rules and forms, and that such information is accumulated and communicated to our management, including our chief executive officer and principal financial and accounting officer, as appropriate, to allow timely decisions regarding required disclosure.

As of June 30, 2015, we have evaluated, under the supervision and with the participation of our management, including the chief executive officer and the principal financial and accounting officer, the effectiveness of the design and operation of our disclosure controls and procedures pursuant to Exchange Act Rule 13a-15. Our management recognizes that any controls and procedures, no matter how well designed and operated, can provide only reasonable assurance of achieving their objectives, and management necessarily applies its judgment in evaluating the cost-benefit relationship of possible controls and procedures. Based upon our evaluation, the chief executive officer and the principal financial and accounting officer concluded that our disclosure controls and procedures were effective. Accordingly, management believes that the condensed consolidated financial statements included in this report fairly present in all material respects our consolidated financial condition, results of operations and cash flow for the periods presented.

Changes in Internal Control over Financial Reporting

During the three and six months ended June 30, 2015, there was no change in our internal control over financial reporting that has materially affected, or is reasonably likely to materially affect, our internal control over financial reporting.

PART II - OTHER INFORMATION

Item 1. Legal Proceedings

We are not currently a party to any material legal proceedings.

Item 1A. Risk Factors

You should carefully review and consider the information regarding certain factors that could materially affect our business, financial condition or future results set forth under Item 1A. (Risk Factors) in our Annual Report on Form 10-K for the fiscal year ended December 31, 2014.

There have been no material changes to the risk factors included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2014, except as follows:

Risks Related to Our Business Operations and Industry

Our future success depends on our ability to retain key executives and to attract, retain and motivate qualified personnel.

22

Our future success depends on our ability to retain our founders and to attract, retain and motivate qualified personnel. We are highly dependent on Christoph Westphal, our President, Chief Executive Officer and Chairman, as well as the other principal members of our management and scientific teams, including our scientific co‑founders, Bruce Bean, Ph.D. and Roderick MacKinnon, M.D., our President, Consumer, Marina Hahn and our Chief Medical Officer, Thomas Wessel, M.D., Ph.D. Although we have employment agreements with Dr. Westphal, Ms. Hahn and Dr. Wessel, such agreements do not prevent them from terminating their employment with us at any time. We do not maintain “key person” insurance for any of our executives or other employees. The loss of the services of any of these persons could impede the achievement of our research, development and commercialization objectives.

Item 2. Unregistered Sales of Equity Securities and Use of Proceeds

Recent sales of unregistered securities.

None.

Use of Proceeds

In February 2015, we completed our initial public offering pursuant to a registration statement on Form S-1 (File No. 333-201276), which the SEC declared effective on January 28, 2015. In our initial public offering, we issued and sold 5,491,191 shares of common stock (inclusive of 91,191 shares of common stock sold by us pursuant to the exercise of an overallotment option granted to the underwriters in connection with the offering) at a public offering price of $16.00 per share, for aggregate gross offering proceeds of $87.9 million. The managing underwriters for our initial public offering were Jefferies LLC, Piper Jaffray & Co., JPM Securities LLC, Cantor Fitzgerald & Co., and Roth Capital Partners, LLC.

The aggregate net proceeds received by us from our initial public offering were $79.9 million, after deducting underwriting discounts and commissions and offering expenses payable by us. No offering expenses were paid directly or indirectly to any of our directors or officers (or their associates) or persons owning 10% or more of any class of our equity securities or to any other affiliates or to any other persons.

There has been no material change in the use of proceeds from our initial public offering as described in our final prospectus dated January 28, 2015 and filed with the SEC pursuant to Rule 424(b)(4) on January 29, 2015.

Item 3. Defaults Upon Senior Securities

Not applicable.

Item 4. Mine Safety Disclosures

Not applicable.

Item 5. Other Information

None.

23

Item 6. Exhibits

EXHIBIT INDEX

Exhibit number		Description of Document
3.1	(1)	Amended and Restated Certificate of Incorporation of the Registrant.
3.2	(1)	Amended and Restated Bylaws of the Registrant.
4.1	(2)	Form of Common Stock Certificate of the Registrant.
4.2	(2)	Amended and Restated Investors' Rights Agreement, dated July 23, 2014, by and among the Registrant and certain of its stockholders.
10.1	+(3)	Executive Employment Agreement, dated as of May 27, 2015, by and between the Company and Christoph Westphal.
10.2	+(3)	Executive Employment Agreement, dated as of May 27, 2015, by and between the Company and John McCabe.
10.3	+(3)	Amendment to Offer Letter, dated May 27, 2015, by and between the Company and Marina Hahn.
10.4	+	Flex Pharma, Inc. Non-Employee Director Compensation Policy, as revised.
31.1		Certification of the Principal Executive Officer pursuant to Rule 13a-14(a) or 15d-14(a) of the Securities Exchange Act of 1934.
31.2		Certification of the Principal Financial Officer pursuant to Rule 13a-14(a) or 15d-14(a) of the Securities Exchange Act of 1934.
32.1		Certification of Principal Executive Officer and Principal Financial Officer pursuant to Rule 13a-14(b) or 15d-14(b) of the Exchange Act and 18 U.S.C. Section 1350.
101		The following materials from Flex Pharma, Inc.'s Quarterly Report on Form 10-Q for the quarter ended June 30, 2015, formatted in XBRL (eXtensible Business Reporting Language):(i) Unaudited Condensed Consolidated Balance Sheets, (ii) Unaudited Condensed Consolidated Statements of Operations and Comprehensive Loss, (iii) Unaudited Condensed Consolidated Statements of Cash Flows, and (iv) Notes to Unaudited Condensed Consolidated Financial Statements.

(1) Incorporated by reference to the Registrant's Current Report on Form 8-K, filed with the SEC on February 9, 2015.

(2) Incorporated by reference to the Registrant's Registration Statement of Form S-1 (File No. 333-201276), as amended.

(3) Incorporated by reference to the Registrant's Current Report on Form 8-K, filed with the SEC on June 2, 2015.

+ Indicates management contract or compensatory plan.

24

SIGNATURES

Pursuant to the requirements of the Securities and Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

	FLEX PHARMA, INC.
	By:	/s/ Christoph Westphal
		Christoph Westphal, M.D., Ph.D. President and Chief Executive Officer
	By:	/s/ John McCabe
		John McCabe Vice President, Finance (Principal Financial and Accounting Officer)
Date: August 5, 2015

25

EX-10.4

FLEX PHARMA, INC.

NON-EMPLOYEE DIRECTOR COMPENSATION POLICY

AS REVISED ON JUNE 29, 2015

Each member of the Board of Directors (the “Board”) who is not also serving as an employee of Flex Pharma, Inc. (“Flex Pharma”) or any of its subsidiaries (each such member, an “Eligible Director”) will receive the compensation described in this Non-Employee Director Compensation Policy for his or her Board service.

This policy will be effective upon the date hereof (the “Effective Date”) and may be amended at any time in the sole discretion of the Board upon recommendation of the Compensation Committee of the Board.

Annual Cash Compensation

The annual cash compensation amount set forth below is payable in equal quarterly installments, payable in arrears on the last day of each fiscal quarter in which the service occurred. If an Eligible Director joins the Board or a committee of the Board at a time other than effective as of the first day of a fiscal quarter, each annual retainer set forth below will be pro-rated based on days served in the applicable fiscal year, with the pro-rated amount paid for the first fiscal quarter in which the Eligible Director provides the service, and regular full quarterly payments thereafter. All annual cash fees are vested upon payment.

1. Annual Board Service Retainer:

a. All Eligible Directors: $40,000

b. Lead Independent Director: $50,000

2. Annual Committee Chair Service Retainer:

a. Chairman of the Audit Committee: $15,000

b. Chairman of the Compensation Committee: $10,000

c. Chairman of the Nominating & Corporate Governance Committee: $7,500

3. Annual Committee Member (other than Committee Chair) Service Retainer:

a. Member of the Audit Committee: $7,500

b. Member of the Compensation Committee: $5,000

c. Member of the Nominating & Corporate Governance Committee: $3,500

Equity Compensation

The equity compensation set forth below will be granted under the Flex Pharma, Inc. 2015 Equity Incentive Plan (the “Plan”). All stock options granted under this policy will be nonstatutory stock options, with an exercise price per share equal to 100% of the Fair Market Value (as defined in the Plan) of the underlying shares of the Company’s Common Stock (the “Common Stock”) on the date of grant, and a term of ten years from the date of grant (subject to earlier termination in connection with a termination of service as provided in the Plan).

1. Initial Grant: On or following each Eligible Director joining the Board, such director will be granted a stock option for 20,000 shares of the Company’s Common Stock, with such options vesting monthly over a period of three years measured from the date of such grant (or such other date as the Board shall otherwise determine).

2. Annual Grant: On the date of each stockholder meeting (or the Board’s June 2015 meeting) each Eligible Director who continues to serve as a non-employee member of the Board on such date will be granted a stock option for 10,000 shares, with such options vesting monthly over one year measured from the date of such grant.

EX-31.1

Exhibit 31.1

Certification Pursuant to Securities Exchange Act Rules 13a-14 and 15d-14 as adopted Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002

I, Christoph Westphal, Chief Executive Officer, certify that:

1. I have reviewed this Quarterly Report on Form 10-Q of Flex Pharma, Inc.;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant's other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:

a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b) Evaluated the effectiveness of the registrant's disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures as of the end of the period covered by this report based on such evaluation; and

c) Disclosed in this report any change in the registrant's internal control over financial reporting that occurred during the registrant's most recent fiscal quarter (the registrant's fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant's internal control over financial reporting.

5. The registrant's other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant's auditors and the audit committee of the registrant's board of directors (or persons performing the equivalent functions):

a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant's ability to record, process, summarize and report financial information; and

b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant's internal control over financial reporting.

	/s/ CHRISTOPH WESTPHAL
	Christoph Westphal, M.D., Ph.D.
August 5, 2015	President and Chief Executive Officer(Principal Executive Officer)

EX-31.2

Exhibit 31.2

Certification Pursuant to Securities Exchange Act Rules 13a-14 and 15d-14 as adopted Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002

I, John McCabe, Vice President of Finance, certify that:

1. I have reviewed this Quarterly Report on Form 10-Q of Flex Pharma, Inc.;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant's other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:

a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b) Evaluated the effectiveness of the registrant's disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures as of the end of the period covered by this report based on such evaluation; and

c) Disclosed in this report any change in the registrant's internal control over financial reporting that occurred during the registrant's most recent fiscal quarter (the registrant's fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant's internal control over financial reporting.

5. The registrant's other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant's auditors and the audit committee of the registrant's board of directors (or persons performing the equivalent functions):

a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant's ability to record, process, summarize and report financial information; and

b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant's internal control over financial reporting.

	/s/ JOHN MCCABE
	John McCabe
August 5, 2015	Vice President, Finance (Principal Financial and Accounting Officer)

EX-32.1

Exhibit 32.1

Certification Pursuant to 18 U.S.C. Section 1350, as Adopted Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002

In connection with the Quarterly Report on Form 10-Q of Flex Pharma, Inc. (the "Company") for the fiscal period ended June 30, 2015 as filed with the Securities and Exchange Commission on the date hereof (the "Report"), the undersigned hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that to the best of their knowledge:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

	/s/ CHRISTOPH WESTPHAL
	Christoph Westphal, M.D., Ph.D.
August 5, 2015	President and Chief Executive Officer(Principal Executive Officer)

	/s/ JOHN MCCABE
	John McCabe
August 5, 2015	Vice President, Finance (Principal Financial and Accounting Officer)

This certification accompanies the Form 10-Q to which it relates, is not deemed filed with the Securities and Exchange Commission and is not to be incorporated by reference into any filing of Flex Pharma, Inc. under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended (whether made before or after the date of the Form 10-Q), irrespective of any general incorporation language contained in such filing.

XML

Common stock - Restricted common stock activity (Details) - 6 months ended Jun. 30, 2015 - Unvested restricted common stock sold to founders - $ / shares	Total
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance, non-vested, number of shares	3,218,590
Vested, number of shares	(508,176)
Ending balance, non-vested, number of shares	2,710,414
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance, weighted average grant date fair value (in usd per share)	$ 0.10
Vested, weighted average grant date fair value (in usd per share)	0.10
Ending balance, weighted average grant date fair value (in usd per share)	$ 0.10

XML

Net loss per share

6 Months Ended

Jun. 30, 2015

Earnings Per Share [Abstract]

Net loss per share

Net loss per share

Basic net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period, determined using the treasury stock method and the if-converted method, for convertible securities, if inclusion of these is dilutive.

Because the Company has reported a net loss for the periods presented, diluted net loss per common share is the same as basic net loss per common share.

The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding for the periods indicated, because including them would have had an anti-dilutive impact:

	As of June 30,
	2015	2014
Unvested restricted common stock sold to founders	2,710,414	3,726,766
Unvested restricted common stock issued upon early exercise of stock options	37,064	—
Options to purchase common stock	1,363,994	297,746
Series A preferred stock	—	15,775,221
Total	4,111,472	19,799,733

XML

Income taxes Income taxes (Details) - USD ($)	3 Months Ended		4 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2015
Income Tax Disclosure [Abstract]
Income tax provision (benefit)	$ 0	$ 0	$ 0	$ 0

XML

Stock-based compensation - Summary of stock-based compensation expense (Details) - USD ($)	3 Months Ended		4 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2015
Employee Service Share-Based Compensation Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,640,559	$ 308,749	$ 320,684	$ 3,386,319
Research and development
Employee Service Share-Based Compensation Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	855,083	95,493	102,051	1,812,293
General and administrative
Employee Service Share-Based Compensation Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 785,476	$ 213,256	$ 218,633	$ 1,574,026

XML

Cash equivalents

6 Months Ended

Jun. 30, 2015

Cash and Cash Equivalents [Abstract]

Cash equivalents

Cash equivalents

Management determines the appropriate classification of marketable securities at the time they are acquired and evaluates the appropriateness of such classifications at each balance sheet date. The Company classifies its marketable securities as available-for-sale pursuant to ASC 320, Investments - Debt and Equity Securities. Marketable securities are recorded at fair value, with unrealized gains and losses included as a component of accumulated other comprehensive income (loss) in the consolidated statement of convertible preferred stock and stockholders’ equity (deficit) and a component of total comprehensive loss in the consolidated statements of operations and comprehensive loss, until realized. Realized gains and losses are included in the consolidated statement of operations and comprehensive loss as part of interest income, net, on a specific-identification basis.

The Company reviews marketable securities for other-than-temporary impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable within a reasonable period of time. Other-than-temporary impairments of investments are recognized in the consolidated statement of operations if the Company has experienced a credit loss, has the intent to sell the marketable security, or if it is more likely than not that the Company will be required to sell the marketable security before recovery of the amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and the duration of the impairment and changes in value subsequent to the end of the period.

Investments classified as current have maturities of less than one year. Investments classified as non-current are those that (i) have a maturity greater than one year and (ii) management does not intend to liquidate within the next year, although these funds are available for use and therefore classified as available-for-sale.

The Company considers all highly liquid investments with maturities of three months or less when purchased to be cash equivalents. During the second quarter of 2015, the Company purchased corporate debt securities in the form of commercial paper and senior corporate notes, all of which were originally classified as cash equivalents and matured prior to June 30, 2015. Cash equivalents as of June 30, 2015 consisted of money market funds, and the Company did not have cash equivalents as of December 31, 2014.

There were no unrealized gains or losses during the three or six months ended June 30, 2015, the three months ended June 30, 2014, or during the period from February 26, 2014 (inception) to June 30, 2014. Realized gains recognized during the three and six months ended June 30, 2015 were immaterial and no realized gains or losses were recognized during 2014.

XML

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 106,011,672	$ 33,854,153
Prepaid expenses and other current assets	810,174	370,396
Total current assets	106,821,846	34,224,549
Property and equipment, net	118,992	85,144
Deferred IPO issuance costs	0	1,074,794
Deferred tax assets	50,103	50,103
Other assets	85,200	50,000
Restricted cash	126,835	126,808
Total assets	107,202,976	35,611,398
Current liabilities:
Accounts payable	812,321	578,653
Accrued expenses and other current liabilities	1,229,351	416,524
Deferred tax liabilities	50,103	50,103
Deferred rent, current portion	21,881	21,881
Total current liabilities	2,113,656	1,067,161
Deferred rent, net of current portion	27,527	35,968
Other long term liabilities	415,442	15,442
Total liabilities	2,556,625	1,118,571
Convertible preferred stock:
Preferred stock, carrying value	0	0
Stockholders' equity (deficit):
Common stock, $0.0001 par value; 100,000,000 and 61,000,000 shares authorized at June 30, 2015 and December 31, 2014, respectively, 17,938,334 and 5,434,301 shares issued at June 30, 2015 and December 31, 2014, respectively, and 15,190,856 and 2,215,711 shares outstanding at June 30, 2015 and December 31, 2014, respectively	1,519	221
Additional paid-in capital	125,751,671	1,472,299
Accumulated deficit	(21,106,839)	(8,010,860)
Total stockholders' equity (deficit)	104,646,351	(6,538,340)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	107,202,976	35,611,398
Series A convertible preferred stock
Convertible preferred stock:
Preferred stock, carrying value	0	15,637,032
Series B Preferred Stock
Convertible preferred stock:
Preferred stock, carrying value	$ 0	$ 25,394,135

XML

Organization and operations

6 Months Ended

Jun. 30, 2015

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Organization and operations

Organization and operations

The Company

Flex Pharma, Inc. (the "Company") is a biotechnology company that was incorporated in Delaware on February 26, 2014 and has a principal place of business in Boston, Massachusetts. The Company is developing innovative and proprietary treatments for nocturnal leg cramps and spasms associated with severe neuromuscular conditions. The Company believes that the chemical neuro-stimulation of certain receptors in primary sensory neurons by our proprietary treatment reduces the repetitive firing, or hyperexcitability, of alpha-motor neurons, thereby preventing or reducing the frequency and intensity of muscle cramps and spasms.

The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, risks of failure of pre-clinical studies, clinical studies and clinical trials, the need to obtain marketing approval for its drug product candidates, the need to successfully commercialize and gain market acceptance of its drug product candidates and its consumer products, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and ability to transition from pilot-scale manufacturing to large-scale production of products.

In February 2015, the Company sold 5,491,191 shares of common stock (inclusive of 91,191 shares of common stock sold by the Company pursuant to the exercise of an overallotment option granted to the underwriters in connection with the offering) through an underwritten initial public offering ("IPO") at a price of $16.00 per share. The aggregate net proceeds received by the Company from the offering were approximately $79,900,000, after deducting underwriting discounts and commissions and offering expenses payable by the Company of approximately $8,000,000 (See Note 2).

Liquidity

The Company has incurred an accumulated deficit of $21,106,839 since inception and will require substantial additional capital to fund its research and development and the launch and growth of its consumer brand. The Company had cash and cash equivalents of $106,011,672 at June 30, 2015. The Company believes its existing cash and cash equivalents will be sufficient to allow the Company to fund its current operating plan for at least the next 12 months.

XML

Net loss per share (Details) - shares	4 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	19,799,733	4,111,472
Unvested restricted common stock sold to founders
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,726,766	2,710,414
Unvested restricted common stock issued upon early exercise of stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	37,064
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	297,746	1,363,994
Series A preferred stock | Preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	15,775,221	0

XML

Common stock - Narrative (Details) - USD ($)	1 Months Ended		3 Months Ended	4 Months Ended	6 Months Ended
	Apr. 30, 2014	Mar. 31, 2014	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized					100,000,000	61,000,000
Common stock, par value (in usd per share)					$ 0.0001	$ 0.0001
Proceeds from sale of restricted common stock to founders				$ 2,321	$ 0
Shares exercised					41,734
Shares exercised, weighted-average exercise price (in usd per share)					$ 9.65
Proceeds from early exercise of stock options					$ 400,000
Unvested restricted common stock sold to founders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock, shares sold	867,314	4,553,415
Restricted common stock, price per share (in usd per share)		$ 0.0004
Proceeds from sale of restricted common stock to founders		$ 1,950
Restricted common stock, repurchase period					90 days
Restricted common stock, repurchase price (in usd per share)					$ 0.0004
Restricted common stock, shares outstanding					2,710,315
Employee stock option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares exercised			37,064
Shares exercised, weighted-average exercise price (in usd per share)			$ 10.79
Vests upon issuance | Unvested restricted common stock sold to founders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock, percent vested					25.00%
Vests ratably over four years | Unvested restricted common stock sold to founders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock, percent vested					75.00%
Restricted common stock, vesting period					4 years

XML

Summary of significant accounting policies and recent accounting pronouncements

6 Months Ended

Jun. 30, 2015

Accounting Policies [Abstract]

Summary of significant accounting policies and recent accounting pronouncements

Summary of significant accounting policies and recent accounting pronouncements

The accompanying unaudited condensed consolidated financial statements reflect the application of certain significant accounting policies as described below and elsewhere in these notes to the condensed consolidated financial statements. As of June 30, 2015, the Company’s significant accounting policies, which are detailed in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2014 (the “2014 10-K”), have not changed.

Unaudited interim financial information

Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the 2014 10-K.

The condensed consolidated financial statements as of June 30, 2015, for the three months ended June 30, 2015 and 2014, for the six months ended June 30, 2015, and for the period from February 26, 2014 (inception) through June 30, 2014, and the related information contained within the notes to the condensed consolidated financial statements, are unaudited. The unaudited condensed consolidated financial statements have been prepared on the same basis as annual audited consolidated financial statements, and in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s condensed consolidated financial position as of June 30, 2015, the condensed consolidated statements of operations and comprehensive loss for the three-and six-month periods ended June 30, 2015, the condensed consolidated statement of cash flows for the six-month period ended June 30, 2015, the condensed consolidated statement of operations and comprehensive loss for the three-month period ended June 30, 2014, and the condensed consolidated statements of operations and comprehensive loss and cash flows for the period from February 26, 2014 (inception) to June 30, 2014. The results for the three and six months ended June 30, 2015 are not necessarily indicative of results to be expected for the year ending December 31, 2015, or any other future annual or interim periods.

Initial public offering

On February 3, 2015, the Company completed its IPO, whereby the Company sold 5,491,191 shares of its common stock (inclusive of 91,191 shares of common stock sold by the Company pursuant to the exercise of an overallotment option granted to the underwriters in connection with the IPO) at a price of $16.00 per share. The shares began trading on the Nasdaq Global Market on January 29, 2015. The aggregate net proceeds received by the Company from the IPO were approximately $79,900,000, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. Upon the closing of the IPO, all outstanding shares of convertible preferred stock converted into 6,971,108 shares of common stock. Additionally, the Company is now authorized to issue 100,000,000 shares of common stock.

Deferred IPO issuance costs, which primarily consisted of direct incremental legal and accounting fees related to the Company's IPO, were previously capitalized at December 31, 2014. Upon the closing of the IPO in February 2015, IPO issuance costs, which totaled $1,848,737, were offset against the IPO proceeds within additional paid-in capital.

Reverse stock split

On January 15, 2015, the Company effected a one-for-4.2825 reverse stock split of its issued and outstanding common stock. All share and per share amounts related to issued and outstanding common stock and stock options included in the Company's condensed consolidated financial statements and notes to the condensed consolidated financial statements have been retroactively adjusted for all periods presented to reflect this reverse stock split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in-capital. The conversion ratios of the Company's previously outstanding shares of convertible preferred stock were also adjusted to reflect the reverse stock split.

Basis of presentation and use of estimates

The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP"). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification ("ASC") and Accounting Standards Update ("ASU") of the Financial Accounting Standards Board ("FASB"). The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company's management evaluates its estimates, which include, but are not limited to, estimates related to clinical study accruals, stock-based compensation expense, and amounts of expenses during the reported period. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.

Prior to the completion of its IPO in February 2015, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company utilized various valuation methodologies in accordance with the framework of the 2004 and 2013 American Institute of Certified Public Accountants Technical Practice Aids, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology included estimates and assumptions that required the Company's judgment. These estimates and assumptions included a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company's common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or a sale of the Company. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date and materially affect the financial statements.

Principles of consolidation

The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, TK Pharma, Inc., a Massachusetts securities corporation. All significant intercompany balances and transactions have been eliminated in consolidation.

Recent accounting pronouncements

In May 2014, the FASB issued ASU No. 2014-09, "Revenue from Contracts with Customers (Topic 606)". The ASU provides for a single comprehensive model for use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The accounting standard is effective for interim and annual periods beginning after December 15, 2016 with no early adoption permitted. In April 2015, the FASB proposed a one year deferral of the effective date of this accounting update to annual periods beginning after December 15, 2017, along with an option to permit early adoption. The Company is required to adopt the amendments in the ASU using one of two acceptable methods: retrospectively to all prior reporting periods presented, with certain practical expedients permitted; or retrospectively with the cumulative effect of initially adopting the ASU recognized at the date of initial application. The Company is currently in the process of evaluating the impact of the guidance related to the Company's anticipated launch of its consumer product in the first half of 2016.

In June 2014, the FASB issued ASU No. 2014-10 "Development Stage Entities (Topic 915): Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation". Under this ASU, the definition of a development stage entity was removed from the ASC, thereby removing the financial reporting distinction between development stage entities and other reporting entities under GAAP. This standard is effective for annual reporting periods beginning after December 15, 2014. Early adoption is permitted for certain entities. The Company was eligible for early adoption and adopted this standard in the accompanying financial statements.

In August 2014, the FASB issued ASU No. 2014-15 "Presentation of Financial Statements - Going Concern (Subtopic 205-40)". The ASU requires all entities to evaluate for the existence of conditions or events that raise substantial doubt about the entity's ability to continue as a going concern within one year after the issuance date of the financial statements. The accounting standard is effective for interim and annual periods ending after December 15, 2016, and will not have a material impact on the consolidated financial statements, but may impact the Company's footnote disclosures.

In February 2015, the FASB issued ASU No. 2015-02 "Consolidation (Topic 810): Amendments to the Consolidation Analysis." ASU 2015-02 changes the analysis that a reporting entity must perform to determine whether it should consolidate certain types of legal entities. It is effective for annual reporting periods, and interim periods within those years, beginning after December 15, 2015. Early adoption is permitted, including adoption in an interim period. The Company is currently in the process of evaluating the impact of the adoption of ASU 2015-02 on its consolidated financial statements.

The Company believes that the impact of other recently issued standards that are not yet effective will not have a material effect on its consolidated financial position or results of operations upon adoption.

XML

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Jun. 30, 2015	Dec. 31, 2014
Preferred stock, par value (in usd per share)	$ 0.0001	$ 0
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	61,000,000
Common stock, shares issued	17,938,334	5,434,301
Common stock, shares outstanding	15,190,856	2,215,711
Series A preferred stock
Preferred stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	16,000,000
Preferred stock, shares issued	0	15,775,221
Preferred stock, shares outstanding	0	15,775,221
Series B Preferred Stock
Preferred stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	14,500,000
Preferred stock, shares issued	0	14,078,647
Preferred stock, shares outstanding	0	14,078,647

XML

Common stock Common stock (Tables)

6 Months Ended

Jun. 30, 2015

Equity [Abstract]

Restricted common stock activity

The following is a summary of restricted common stock activity related to shares sold to the Company's founders:

	Number of Shares		Weighted-Average Grant Date Fair Value
Non-vested at December 31, 2014	3,218,590		$	0.10
Vested	(508,176	)	0.10
Non-vested at June 30, 2015	2,710,414		$	0.10

XML

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2015	Jul. 31, 2015
Document And Entity Information [Abstract]
Entity Registrant Name	Flex Pharma, Inc.
Entity Central Index Key	0001615219
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		17,938,334

XML

Stock-based compensation (Tables)

6 Months Ended

Jun. 30, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of stock option activity

The following table summarizes stock option activity for employees and non-employees for the six months ended June 30, 2015:

	Shares		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2014	926,832		$	3.40
Granted	505,748		15.02
Exercised	(41,734	)	9.65
Cancelled or forfeited	(26,852	)	9.48
Outstanding at June 30, 2015	1,363,994		$	7.40	9.37	$	13,527,657
Exercisable at June 30, 2015	98,024		$	1.51	8.93	$	1,538,006
Vested or expected to vest at June 30, 2015	1,327,695		$	7.38	9.37	$	13,189,776

Summary of stock-based compensation expense

Total stock-based compensation expense recognized for employee and non-employee restricted common stock, and stock options granted to employees and non-employees is included in the Company's condensed consolidated statement of operations and comprehensive loss as follows:

	Three Months Ended June 30, 2015		Three Months Ended June 30, 2014		Six Months Ended June 30, 2015		Period from February 26, 2014 (Inception) to June 30, 2014
Research and development	$	855,083	$	95,493	$	1,812,293	$	102,051
General and administrative	785,476		213,256		1,574,026		218,633
Total	$	1,640,559	$	308,749	$	3,386,319	$	320,684

XML

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($)	3 Months Ended		4 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2015
Operating expenses:
Research and development	$ 3,190,178	$ 1,099,644	$ 1,129,667	$ 5,995,124
General and administrative	3,904,403	1,092,665	1,155,365	7,120,615
Total operating expenses	7,094,581	2,192,309	2,285,032	13,115,739
Loss from operations	(7,094,581)	(2,192,309)	(2,285,032)	(13,115,739)
Interest income, net	16,183	2,658	2,658	19,760
Net loss	(7,078,398)	(2,189,651)	(2,282,374)	(13,095,979)
Comprehensive loss	$ (7,078,398)	$ (2,189,651)	$ (2,282,374)	$ (13,095,979)
Net loss per share attributable to common stockholders - basic and diluted (in usd per share)	$ (0.47)	$ (1.42)	$ (1.53)	$ (1.04)
Weighted-average number of common shares outstanding — basic and diluted	15,034,764	1,539,463	1,493,403	12,620,771

XML

Stock-based compensation

6 Months Ended

Jun. 30, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-based compensation

Stock-based compensation

In March 2014, the Company adopted the Flex Pharma, Inc. 2014 Equity Incentive Plan (the "2014 Plan"), under which it had the ability to grant incentive stock options, non-qualified stock options, restricted stock awards, restricted stock units and stock appreciation rights to purchase up to 116,754 shares of common stock. In April 2014, the Company amended the 2014 Plan to reserve for the issuance of up to 1,451,087 shares of common stock pursuant to equity awards. In September 2014, the Company further amended the 2014 Plan to reserve for the issuance of up to 2,070,200 shares of common stock pursuant to equity awards. Terms of stock award agreements, including vesting requirements, were determined by the board of directors, subject to the provisions of the 2014 Plan. For options granted under the 2014 Plan, the exercise price equaled the fair market value of the common stock as determined by the board of directors on the date of grant. No further awards will be granted under the 2014 Plan.

In January 2015, the Company's board of directors adopted, and the Company's stockholders approved, the 2015 Equity Incentive Plan (the "2015 Plan"), which became effective immediately prior to the closing of the Company's IPO. The 2015 Plan provides for the grant of incentive stock options ("ISOs"), nonstatutory stock options, restricted stock awards, restricted stock units, stock appreciation rights, performance-based stock awards, and other stock-based awards. Additionally, the 2015 Plan provides for the grant of performance-based cash awards. ISOs may be granted only to the Company's employees. All other awards may be granted to the Company's employees, including officers, and to non-employee directors and consultants. As of June 30, 2015, there were 673,080 shares remaining available for the grant of stock awards under the 2015 Plan.

The Company has awarded stock options to its employees, directors, advisors and consultants, pursuant to the plans described above. Stock options subsequent to the completion of the Company's IPO are granted with an exercise price equal to the closing market price of the Company's common stock on the date of grant. Stock options generally vest over one to four years and have a contractual term of ten years. Stock options are valued using the Black-Scholes option pricing model and compensation cost is recognized based on the resulting value over the service period. Unvested awards to non-employees are re-measured at each vest date and at each financial reporting date. The following table summarizes stock option activity for employees and non-employees for the six months ended June 30, 2015:

	Shares		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2014	926,832		$	3.40
Granted	505,748		15.02
Exercised	(41,734	)	9.65
Cancelled or forfeited	(26,852	)	9.48
Outstanding at June 30, 2015	1,363,994		$	7.40	9.37	$	13,527,657
Exercisable at June 30, 2015	98,024		$	1.51	8.93	$	1,538,006
Vested or expected to vest at June 30, 2015	1,327,695		$	7.38	9.37	$	13,189,776

Total stock-based compensation expense recognized for employee and non-employee restricted common stock, and stock options granted to employees and non-employees is included in the Company's condensed consolidated statement of operations and comprehensive loss as follows:

	Three Months Ended June 30, 2015		Three Months Ended June 30, 2014		Six Months Ended June 30, 2015		Period from February 26, 2014 (Inception) to June 30, 2014
Research and development	$	855,083	$	95,493	$	1,812,293	$	102,051
General and administrative	785,476		213,256		1,574,026		218,633
Total	$	1,640,559	$	308,749	$	3,386,319	$	320,684

As of June 30, 2015, there was approximately $20,334,155 of total unrecognized compensation cost related to non-vested equity awards. Total unrecognized compensation cost will be adjusted for the re-measurement of non-employee awards as well as future changes in employee and non-employee forfeitures, if any. The Company expects to recognize that cost over a remaining weighted-average period of 2.87 years.

Employee stock purchase plan

In January 2015, the Company's board of directors adopted, and the Company's stockholders approved, the 2015 Employee Stock Purchase Plan (the "ESPP"), which became effective upon the date of execution of the underwriting agreement pursuant to which the Company's common stock was priced in connection with the IPO. As of June 30, 2015, the Company had not yet instituted any offering periods under the ESPP and no shares of the Company's common stock have been purchased under the ESPP.

XML

Common stock

6 Months Ended

Jun. 30, 2015

Equity [Abstract]

Common stock

Common stock

As of June 30, 2015, the Company had authorized 100,000,000 shares of common stock, $0.0001 par value per share. Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors.

Restricted common stock

In March 2014, the Company sold 4,553,415 shares of restricted common stock to the founders of the Company ("recipients"), for $0.0004 per share, for total proceeds of $1,950. In April 2014, based upon anti-dilution provisions granted to the recipients, an additional 867,314 shares of restricted common stock were sold to the same recipients, after which the anti-dilution provisions were terminated. The restricted common stock vested 25% upon issuance, and the remaining 75% vests ratably over four years, during which time the Company has the right to repurchase the unvested shares held by a recipient if the relationship between such recipient and the Company ceases. If the relationship terminates, the Company has 90 days to repurchase unvested shares at $0.0004 per share. Such shares are not accounted for as outstanding until they vest. As of June 30, 2015, 2,710,315 shares of restricted common stock had vested and are accounted for as outstanding common stock. Unvested restricted common stock awards to non-employees are re-measured at each vest date and each financial reporting date.

The following is a summary of restricted common stock activity related to shares sold to the Company's founders:

	Number of Shares		Weighted-Average Grant Date Fair Value
Non-vested at December 31, 2014	3,218,590		$	0.10
Vested	(508,176	)	0.10
Non-vested at June 30, 2015	2,710,414		$	0.10

Early exercise of stock options

During the first quarter of 2015, 37,064 employee stock options, with a weighted-average grant date fair value of $10.79 per share, were exercised pursuant to an early exercise provision in an employee's stock option agreement. None of the exercised options had vested as of June 30, 2015, and the early exercise provision contains a repurchase option by the Company. Accordingly, the $400,000 of exercise proceeds received by the Company are being accounted for as a liability on the Company's condensed consolidated balance sheet at June 30, 2015. The proceeds received will remain classified as a liability and the related shares will not be considered outstanding, for accounting purposes, until the shares vest in the fourth quarter of 2015.

XML

Accrued expenses and other current liabilities (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Payroll and employee-related costs	$ 675,598	$ 34,218
Research and development costs	275,764	125,067
Professional fees	153,584	15,500
Consumer brand-related costs	77,149	23,635
Other	47,256	42,955
Deferred IPO issuance costs	0	175,149
Total	$ 1,229,351	$ 416,524

XML

Organization and operations (Details) - USD ($)		4 Months Ended	6 Months Ended
	Feb. 03, 2015	Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014	Feb. 26, 2014
Subsidiary, Sale of Stock [Line Items]
Proceeds from initial public offering, net of offering costs	$ 79,900,000	$ 0	$ 80,435,430
Underwriting discounts, commissions, and offering expenses	$ 8,000,000
Retained earnings (accumulated deficit)			(21,106,839)	$ (8,010,860)
Cash and cash equivalents		$ 14,287,264	$ 106,011,672	$ 33,854,153	$ 0
IPO
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued	5,491,191
Common stock, price per share (in usd per share)	$ 16.00
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued	91,191

XML

Net loss per share (Tables)

6 Months Ended

Jun. 30, 2015

Earnings Per Share [Abstract]

Schedule of antidilutive securities excluded from computation of earnings per share

The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding for the periods indicated, because including them would have had an anti-dilutive impact:

	As of June 30,
	2015	2014
Unvested restricted common stock sold to founders	2,710,414	3,726,766
Unvested restricted common stock issued upon early exercise of stock options	37,064	—
Options to purchase common stock	1,363,994	297,746
Series A preferred stock	—	15,775,221
Total	4,111,472	19,799,733

XML

Income taxes

6 Months Ended

Jun. 30, 2015

Income Tax Disclosure [Abstract]

Income tax provision (benefit)

Income taxes

Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Based upon the Company's history of operating losses and the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets. There was no significant income tax provision or benefit for the three or six months ended June 30, 2015, for the three months ended June 30, 2014 or for the period from February 26, 2014 (inception) to June 30, 2014.

XML

Summary of significant accounting policies and recent accounting pronouncements (Policies)

6 Months Ended

Jun. 30, 2015

Accounting Policies [Abstract]

Basis of presentation

The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP"). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification ("ASC") and Accounting Standards Update ("ASU") of the Financial Accounting Standards Board ("FASB").

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company's management evaluates its estimates, which include, but are not limited to, estimates related to clinical study accruals, stock-based compensation expense, and amounts of expenses during the reported period. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.

Prior to the completion of its IPO in February 2015, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company utilized various valuation methodologies in accordance with the framework of the 2004 and 2013 American Institute of Certified Public Accountants Technical Practice Aids, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology included estimates and assumptions that required the Company's judgment. These estimates and assumptions included a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company's common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or a sale of the Company. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date and materially affect the financial statements.

Principles of consolidation

Principles of consolidation

The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, TK Pharma, Inc., a Massachusetts securities corporation. All significant intercompany balances and transactions have been eliminated in consolidation.

Recent accounting pronouncements

Recent accounting pronouncements

In May 2014, the FASB issued ASU No. 2014-09, "Revenue from Contracts with Customers (Topic 606)". The ASU provides for a single comprehensive model for use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The accounting standard is effective for interim and annual periods beginning after December 15, 2016 with no early adoption permitted. In April 2015, the FASB proposed a one year deferral of the effective date of this accounting update to annual periods beginning after December 15, 2017, along with an option to permit early adoption. The Company is required to adopt the amendments in the ASU using one of two acceptable methods: retrospectively to all prior reporting periods presented, with certain practical expedients permitted; or retrospectively with the cumulative effect of initially adopting the ASU recognized at the date of initial application. The Company is currently in the process of evaluating the impact of the guidance related to the Company's anticipated launch of its consumer product in the first half of 2016.

In June 2014, the FASB issued ASU No. 2014-10 "Development Stage Entities (Topic 915): Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation". Under this ASU, the definition of a development stage entity was removed from the ASC, thereby removing the financial reporting distinction between development stage entities and other reporting entities under GAAP. This standard is effective for annual reporting periods beginning after December 15, 2014. Early adoption is permitted for certain entities. The Company was eligible for early adoption and adopted this standard in the accompanying financial statements.

In August 2014, the FASB issued ASU No. 2014-15 "Presentation of Financial Statements - Going Concern (Subtopic 205-40)". The ASU requires all entities to evaluate for the existence of conditions or events that raise substantial doubt about the entity's ability to continue as a going concern within one year after the issuance date of the financial statements. The accounting standard is effective for interim and annual periods ending after December 15, 2016, and will not have a material impact on the consolidated financial statements, but may impact the Company's footnote disclosures.

In February 2015, the FASB issued ASU No. 2015-02 "Consolidation (Topic 810): Amendments to the Consolidation Analysis." ASU 2015-02 changes the analysis that a reporting entity must perform to determine whether it should consolidate certain types of legal entities. It is effective for annual reporting periods, and interim periods within those years, beginning after December 15, 2015. Early adoption is permitted, including adoption in an interim period. The Company is currently in the process of evaluating the impact of the adoption of ASU 2015-02 on its consolidated financial statements.

The Company believes that the impact of other recently issued standards that are not yet effective will not have a material effect on its consolidated financial position or results of operations upon adoption.

Cash equivalents

Cash equivalents

Management determines the appropriate classification of marketable securities at the time they are acquired and evaluates the appropriateness of such classifications at each balance sheet date. The Company classifies its marketable securities as available-for-sale pursuant to ASC 320, Investments - Debt and Equity Securities. Marketable securities are recorded at fair value, with unrealized gains and losses included as a component of accumulated other comprehensive income (loss) in the consolidated statement of convertible preferred stock and stockholders’ equity (deficit) and a component of total comprehensive loss in the consolidated statements of operations and comprehensive loss, until realized. Realized gains and losses are included in the consolidated statement of operations and comprehensive loss as part of interest income, net, on a specific-identification basis.

The Company reviews marketable securities for other-than-temporary impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable within a reasonable period of time. Other-than-temporary impairments of investments are recognized in the consolidated statement of operations if the Company has experienced a credit loss, has the intent to sell the marketable security, or if it is more likely than not that the Company will be required to sell the marketable security before recovery of the amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and the duration of the impairment and changes in value subsequent to the end of the period.

Investments classified as current have maturities of less than one year. Investments classified as non-current are those that (i) have a maturity greater than one year and (ii) management does not intend to liquidate within the next year, although these funds are available for use and therefore classified as available-for-sale.

The Company considers all highly liquid investments with maturities of three months or less when purchased to be cash equivalents.

XML

Accrued expenses and other current liabilities (Tables)

6 Months Ended

Jun. 30, 2015

Payables and Accruals [Abstract]

Schedule of accrued expenses

Accrued expenses and other current liabilities consisted of the following:

	June 30, 2015		December 31, 2014
Payroll and employee-related costs	$	675,598	$	34,218
Research and development costs	275,764		125,067
Professional fees	153,584		15,500
Consumer brand-related costs	77,149		23,635
Other	47,256		42,955
Deferred IPO issuance costs	—		175,149
Total	$	1,229,351	$	416,524

Schedule of other current liabilities

Accrued expenses and other current liabilities consisted of the following:

	June 30, 2015		December 31, 2014
Payroll and employee-related costs	$	675,598	$	34,218
Research and development costs	275,764		125,067
Professional fees	153,584		15,500
Consumer brand-related costs	77,149		23,635
Other	47,256		42,955
Deferred IPO issuance costs	—		175,149
Total	$	1,229,351	$	416,524

XML

Cash equivalents Cash equivalents (Details) - USD ($)	3 Months Ended	4 Months Ended	6 Months Ended	10 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Abstract]
Unrealized gains (losses)	$ 0	$ 0	$ 0
Realized gain (loss)				$ 0

XML

Stock-based compensation - Narrative (Details) - USD ($)	6 Months Ended
	Jun. 30, 2015	Sep. 30, 2014	Apr. 30, 2014	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 20,334,155
Unrecognized compensation cost, recognition period	2 years 10 months 13 days
Flex Pharma, Inc. 2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized		2,070,200	1,451,087	116,754
2015 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares remaining available for grant of stock awards	673,080
Employee stock option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, contractual term	10 years
Minimum | Employee stock option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, vesting period	1 year
Maximum | Employee stock option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, vesting period	4 years

XML

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($)	4 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2015
Operating activities
Net loss	$ (2,282,374)	$ (13,095,979)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,981	20,714
Stock-based compensation expense	320,684	3,386,319
Other non-cash items	55,221	0
Changes in operating assets and liabilities:
Restricted cash	(126,595)	(27)
Prepaid expenses and other current assets	(69,223)	(439,778)
Other assets	0	(35,200)
Accounts payable	399,888	558,068
Accrued expenses and other current liabilities	374,332	1,008,976
Deferred rent	48,190	(8,441)
Other long term liabilities	15,442	0
Net cash used in operating activities	(1,262,454)	(8,605,348)
Investing activities
Purchases of property and equipment	(34,414)	(75,562)
Net cash used in investing activities	(34,414)	(75,562)
Financing activities
Proceeds from initial public offering, net of offering costs	0	80,435,430
Proceeds from issuance of Series A convertible preferred stock, net of issuance costs	15,581,811	0
Proceeds from sale of restricted common stock to founders	2,321	0
Proceeds from exercise of stock options	0	402,999
Net cash provided by financing activities	15,584,132	80,838,429
Net increase in cash and cash equivalents	14,287,264	72,157,519
Cash and cash equivalents at beginning of period		33,854,153
Cash and cash equivalents at end of period	14,287,264	106,011,672
Supplemental cash flow information
Deferred IPO issuance costs in accounts payable and accrued expenses at December 31, 2014	0	499,549
Property and equipment in accrued expenses at December 31, 2014	0	21,000
IPO issuance costs paid in cash through December 31, 2014		575,245
Issuance of Series A convertible preferred stock in satisfaction of accounts payable	$ 55,221	$ 0

XML

Accrued expenses and other current liabilities

6 Months Ended

Jun. 30, 2015

Payables and Accruals [Abstract]

Accrued expenses and other current liabilities

Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:

	June 30, 2015		December 31, 2014
Payroll and employee-related costs	$	675,598	$	34,218
Research and development costs	275,764		125,067
Professional fees	153,584		15,500
Consumer brand-related costs	77,149		23,635
Other	47,256		42,955
Deferred IPO issuance costs	—		175,149
Total	$	1,229,351	$	416,524

XML

Stock-based compensation - Summary of stock option activity (Details) - USD ($)	6 Months Ended
	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares outstanding, Beginning Balance	926,832
Shares granted	505,748
Shares exercised	(41,734)
Shares canceled or forfeited	(26,852)
Shares outstanding, Ending Balance	1,363,994
Shares exercisable	98,024
Shares vested or expected to vest	1,327,695
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Shares outstanding, weighted-average exercise price, Ending Balance (in usd per share)	$ 3.40
Shares granted, weighted-average exercise price (in usd per share)	15.02
Shares exercised, weighted-average exercise price (in usd per share)	9.65
Shares canceled or forfeited, weighted-average exercise price (in usd per share)	9.48
Shares outstanding, weighted-average exercise price, Beginning Balance (in usd per share)	7.40
Shares exercisable, weighted-average exercise price (in usd per share)	1.51
Shares vested or expected to vest, weighted-average exercise price (in usd per share)	$ 7.38
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, weighted-average remaining contractual term	9 years 4 months 13 days
Exercisable, weighted-average remaining contractual term	8 years 11 months 5 days
Vested or expected to vest, weighted-average remaining contractual term	9 years 4 months 13 days
Outstanding, aggregate intrinsic value	$ 13,527,657
Exercisable, aggregate intrinsic value	1,538,006
Vested or expected to vest, aggregate intrinsic value	$ 13,189,776

XML

Summary of significant accounting policies and recent accounting pronouncements - Narrative (Details)			4 Months Ended	6 Months Ended
	Feb. 03, 2015 USD ($) $ / shares shares	Jan. 15, 2015	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) shares	Dec. 31, 2014 shares
Subsidiary, Sale of Stock [Line Items]
Proceeds from initial public offering, net of offering costs | $	$ 79,900,000		$ 0	$ 80,435,430
Common stock, number of shares issued from conversion of preferred stock (in shares)	6,971,108
Common stock, shares authorized				100,000,000	61,000,000
IPO issuance cost | $	$ 1,848,737
Reverse stock split conversion ratio		0.2335
IPO
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued	5,491,191
Common stock, price per share (in usd per share) | $ / shares	$ 16.00
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued	91,191