Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form S-3 of our report dated March 10, 2017 relating to the consolidated financial statements, which appears in Flexion Therapeutics Inc.’s Annual Report on Form 10-K for the year ended December 31, 2016. We also consent to the reference to us under the heading “Experts” in such Registration Statement.

/s/ PricewaterhouseCoopers LLP

Boston, Massachusetts

June 30, 2017