SC TO-I/A

QuickLinks -- Click here to rapidly navigate through this document

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE TO
Tender Offer Statement under Section 14(d)(1) or 13(e)(1) of the Securities Exchange Act of 1934

(Amendment No. 1)

CEPHALON, INC.
(Name of Subject Company (issuer))

CEPHALON, INC.
(Name of Filing Person (offeror))

Zero Coupon Convertible Subordinated Notes
due June 15, 2033, First Putable June 15, 2008

Zero Coupon Convertible Subordinated Notes
due June 15, 2033, First Putable June 15, 2010
(Title of Class of Securities)

156708 AF 6 and 156708 AG 4

156708 AH 2 and 156708 AJ 8
(CUSIP Number of Class of Securities)

John E. Osborn
Senior Vice President, General Counsel
and Secretary
Cephalon, Inc.
145 Brandywine Parkway
West Chester, PA 19380
(610) 344-0200
(Name, Address and Telephone Number of Person Authorized to Receive Notices
and Communications on Behalf of the Person(s) Filing Statement)

Copy to:
Pran Jha
Sidley Austin Brown & Wood LLP
Bank One Plaza
10 South Dearborn Street
Chicago, IL 60603

o

Check box if the filing relates solely to preliminary communications made before the commencement of a tender offer.

Check the appropriate boxes to designate any transactions to which this statement relates:

o  third party tender offer subject to Rule 14d-1	o  going-private transaction subject to Rule 13e-3
ý  issuer tender offer subject to Rule 13e-4	o  amendment to Schedule 13D under Rule 13d-2

        Check the following box if the filing is a final amendment reporting the results of the tender offer. o

        This Amendment No. 1 to Tender Offer Statement on Schedule TO amends and supplements the Tender Offer Statement on Schedule TO filed by Cephalon, Inc., a Delaware corporation (the "Company"), on November 16, 2004 (as amended and supplemented, the "Schedule TO"), relating to an offer by the Company to exchange $1,000 principal amount of the Company's Zero Coupon Convertible Subordinated Notes due June 15, 2033, First Putable June 15, 2008 (the "New 2008 Notes"), for each $1,000 principal amount of validly tendered and accepted outstanding Zero Coupon Convertible Subordinated Notes due June 15, 2033, First Putable June 15, 2008 and issued June 11, 2003 (the "Old 2008 Notes"), of the Company and $1,000 principal amount of the Company's Zero Coupon Convertible Subordinated Notes due June 15, 2033, First Putable June 15, 2010 (the "New 2010 Notes," and together with the New 2008 Notes, the "New Notes"), for each $1,000 principal amount of validly tendered and accepted outstanding Zero Coupon Convertible Subordinated Notes due June 15, 2033, First Putable June 15, 2010 and issued on June 15, 2003 (the "Old 2010 Notes," and together with the Old 2008 Notes, the "Old Notes"), of the Company upon the terms and subject to the conditions contained in the Offer to Exchange dated November 16, 2004 (as amended or supplemented from time to time, the "Offer to Exchange"), a copy of which is attached hereto as Exhibit (a)(1)(i), and the related Letter of Transmittal (the "Letter of Transmittal"), a copy of which is attached hereto as Exhibit (a)(1)(ii) (which together with the Offer to Exchange constitute the "Offer").

Item 1 through Item 11.

        Items 1 through 11 of the Schedule TO are hereby amended and supplemented as follows:

        (1) The first full paragraph on the cover of the Offer to Exchange is hereby amended and restated in its entirety as follows:

        We are offering to exchange our Zero Coupon Convertible Subordinated Notes due June 15, 2033, First Putable June 15, 2008, which we refer to as the "new 2008 notes," for our outstanding Zero Coupon Convertible Subordinated Notes due June 15, 2033, First Putable June 15, 2008, issued on June 11, 2003, which we refer to as the "old 2008 notes," and our Zero Coupon Convertible Subordinated Notes due June 15, 2033, First Putable June 15, 2010, which we refer to as the "new 2010 notes," for our outstanding Zero Coupon Convertible Subordinated Notes due June 15, 2033, First Putable June 15, 2010, issued on June 11, 2003, which we refer to as the "old 2010 notes," on the terms set forth in this offer to exchange and in the accompanying letter of transmittal. We refer to this offer as the "exchange offer." The new 2008 notes and new 2010 notes are referred to together as the "new notes," and the old 2008 notes and old 2010 notes are referred to together as the "old notes."

        (2) The first sentence of the last paragraph under the section entitled "Special Note Regarding Forward-Looking Statements" of the Offer to Exchange is hereby amended and restated in its entirety as follows:

        We do not intend to update publicly an forward-looking statement, whether as a result of new information, future events or otherwise, except as may be required by Rule 13e-4(d)(2) under the Securities Exchange Act of 1934, as amended, or any other applicable law.

        (3) The second sentence of the second paragraph under the section entitled "The Exchange Offer—Exchange Agent" of the Offer to Exchange is hereby amended and restated in its entirety as follows:

        As compensation for its services, the exchange agent will receive a flat fee in a customary amount, will be reimbursed for reasonable out-of-pocket expenses and will be indemnified against liabilities in connection with its services, including liabilities under the federal securities laws.

        (4) The fourth paragraph under the section entitled "Description of the New Notes—Conversion of New Notes—Conversion Upon Satisfaction of Market Price Condition" of the Offer to Exchange is hereby amended and restated in its entirety as follows:

        A "trading day" means any day that is a trading day on Nasdaq or, if our common stock (or relevant securities of a successor obligor) is not listed on Nasdaq, on the principal other national or regional securities exchange on which our common stock (or relevant securities of a successor obligor) is then listed or, if our common stock (or relevant securities of a successor obligor) is not listed on a national or regional securities exchange, on Nasdaq or, if our common stock (or relevant securities of a successor obligor) is not quoted on Nasdaq, on the principal other market on which our common stock (or relevant securities of a successor obligor) is then traded, other than (i) a day on which trading on Nasdaq or such other principal other market on which our common stock (or relevant securities of a successor obligor) is listed, as applicable, is scheduled to close prior to its regular weekday closing time or (ii) a day on which, during the one-half hour period prior to the close of trading on such day, there is a suspension or limitation imposed on trading in our common stock on Nasdaq or such other principal other market on which our common stock (or relevant securities of a successor obligor) is listed, as applicable (by reason of movements in price exceeding limits permitted by that exchange or otherwise).

        (5) The first sentence of the first paragraph under the section entitled "Documents Incorporated by Reference" of the Offer to Exchange is hereby amended and restated in its entirety as follows:

        We are "incorporating by reference" into this offer to exchange certain information that we have filed with the SEC.

Item 5.

        Item 5 of the Schedule TO is hereby amended and restated in its entirety as follows:

        In connection with the issuance of the Old Notes, the Company entered into two convertible note hedges dated as of June 6, 2003 (the "Original Hedges") issued by Credit Suisse First Boston International ("CSFBI"). Pursuant to the Original Hedges, CSFBI will deliver to the Company the number of shares of common stock required to be issued in connection with the conversion of the Old Notes upon payment by the Company to CSFBI of the principal amount of the Old Notes so converted. Alternatively, at the Company's option, CSFBI will deliver cash (or shares of an equivalent value) to the Company in an amount equal to the market value of the shares of common stock required to be issued in connection with the conversion of the Old Notes less the principal amount of the Old Notes so converted. At its option, the Company may settle the Original Hedges in cash. On December 3, 2004, the Company entered into two additional convertible note hedges (the "New Hedges") issued by CSFBI. Under the New Hedges, CSFBI will deliver to the Company upon settlement of the New Hedges the number of shares of the common stock required to be issued in connection with the conversion of the New Notes. The New Hedges replace and supercede the Original Hedges except that, to the extent that Old Notes remain outstanding after consummation of the Offer, the Original Hedges will apply to such Old Notes.

        Pursuant to two separate transactions, the Company issued to CSFBI warrants to purchase 12,939,689 shares of common stock at an exercise price of $72.08 per share. 6,302,521 of the warrants expire on June 15, 2008 and the remaining 6,637,168 warrants expire on June 15, 2010. At its option, the Company may settle the warrants in cash.

        The Original Hedges, the warrants and the New Hedges are included as Exhibits (d)(1), (d)(2), (d)(3), (d)(4), (d)(5) and (d)(6) hereto and incorporated by reference.

2

Item 12. Exhibits.

        Item 12 of the Schedule TO is hereby amended and restated in its entirety as follows:

Exhibit No.	Description
(a)(1)(i)*	Offer to Exchange, dated November 16, 2004.
(a)(1)(ii)*	Letter of Transmittal.
(a)(1)(iii)*	Letter to Brokers, Dealers, Commercial Banks, Trust Companies and other Nominees.
(a)(1)(iv)*	Letter to Clients.
(a)(i)(v)*	Notice of Guaranteed Delivery.
(a)(2)	None.
(a)(3)	None.
(a)(4)	None.
(a)(5)*	Press Release, dated November 16, 2004.
(b)	None.
(d)(1)*	Five Year Convertible Note Hedge, dated June 6, 2003, between the Company and Credit Suisse First Boston International.
(d)(2)*	Seven Year Convertible Note Hedge, dated June 6, 2003, between the Company and Credit Suisse First Boston International.
(d)(3)*	Five Year Warrant, dated June 6, 2003, between the Company and Credit Suisse First Boston International.
(d)(4)*	Seven Year Warrant, dated June 6, 2003, between the Company and Credit Suisse First Boston International.
(d)(5)+	Five Year Convertible Note Hedge, dated December 3, 2004, between the Company and Credit Suisse First Boston International.
(d)(6)+	Seven Year Convertible Note Hedge, dated December 3, 2004, between the Company and Credit Suisse First Boston International.
(g)	None.
(h)	None.

*

Previously filed

+

Filed herewith

3

SIGNATURE

        After due inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

	Cephalon, Inc.
	By:	/s/  J. KEVIN BUCHI Name:  J. Kevin Buchi Title:    Senior Vice President and Chief Financial Officer
Dated: December 13, 2004

4

Exhibit Index

Exhibit No.	Description
(a)(1)(i)*	Offer to Exchange, dated November 16, 2004.
(a)(1)(ii)*	Letter of Transmittal.
(a)(1)(iii)*	Letter to Brokers, Dealers, Commercial Banks, Trust Companies and other Nominees.
(a)(1)(iv)*	Letter to Clients.
(a)(i)(v)*	Notice of Guaranteed Delivery.
(a)(2)	None.
(a)(3)	None.
(a)(4)	None.
(a)(5)*	Press Release, dated November 16, 2004.
(b)	None.
(d)(1)*	Five Year Convertible Note Hedge, dated June 6, 2003, between the Company and Credit Suisse First Boston International.
(d)(2)*	Seven Year Convertible Note Hedge, dated June 6, 2003, between the Company and Credit Suisse First Boston International.
(d)(3)*	Five Year Warrant, dated June 6, 2003, between the Company and Credit Suisse First Boston International.
(d)(4)*	Seven Year Warrant, dated June 6, 2003, between the Company and Credit Suisse First Boston International.
(d)(5)+	Five Year Convertible Note Hedge, dated December 3, 2004, between the Company and Credit Suisse First Boston International.
(d)(6)+	Seven Year Convertible Note Hedge, dated December 3, 2004, between the Company and Credit Suisse First Boston International.
(g)	None.
(h)	None.

*

Previously filed

+

Filed herewith

QuickLinks

Item 1 through Item 11.
Item 5.

Item 12. Exhibits.

SIGNATURE
Exhibit Index

EX-99.(D)(5)

Exhibit 99(d)(5)

CONVERTIBLE NOTE HEDGE
(FIVE YEAR)

December 3, 2004

Cephalon, Inc.
145 Brandywine Parkway
West Chester, PA 19380
Attention: Kevin Buchi, Senior Vice President &
        Chief Financial Officer

Credit Suisse First Boston International
One Cabot Square
London E14 4QJ
England

Dear Sirs:

        In connection with the exchange offer (the "Exchange Offer") expected to be consummated on or about December 16, 2004 of the Issuer's (as defined below) Zero Coupon Convertible Subordinated Notes due June 15, 2033, first putable on June 15, 2008, issued on June 11, 2003 with an original principal amount of $375,000,000 (the "Original Notes"), with the Reference Notes described below, Party A and Party B hereby agree that this letter agreement (this "Confirmation") shall supersede and replace, except to the extent expressly stated below, the confirmation for the Convertible Note Hedge (Five Year), dated June 6, 2003, Reference Number 40046257 (the "Original Confirmation"), between Party A and Party B. This Confirmation constitutes a "Confirmation" as referred to in the Agreement specified below.

1.

The definitions and provisions contained in the 1996 ISDA Equity Derivatives Definitions (the "Equity Definitions") and in the 2000 ISDA Definitions (the "Swap Definitions" and, together with the Equity Definitions, the "Definitions") (in each case as published by the International Swaps and Derivatives Association, Inc.) are incorporated into this Confirmation. In the event of any inconsistency between the Equity Definitions and the Swap Definitions, the Equity Definitions will govern, and between the Definitions and this Confirmation, this Confirmation will prevail. References herein to a "Transaction" shall be deemed to be references to a "Share Option Transaction" for purposes of the Equity Definitions and an "Swap Transaction" for the purposes of the Swap Definitions.

This Transaction (this "Transaction") together with all other Confirmations of Share Transactions between Party A and Party B with respect to Shares of the Issuer contemporaneously or previously entered into between them, notwithstanding anything to the contrary therein, shall supplement, form a part of, and be subject to an ISDA 1992 Master Agreement (Multicurrency—Cross Border) (the "Agreement"), as if, on the Trade Date of the first such Transaction between Party A and Party B, they had executed the Agreement (without any Schedule thereto) and specified that (1) the Automatic Early Termination provisions contained in Section 6(a) of such Agreement would apply, (2) Second Method and Loss would apply, (3) such Agreement would cover only Share Transactions with respect to Shares of the Issuer referred to herein and (4) for purposes of Section 2(c) of such Agreement, references to payments of amounts denominated in the same currency shall be deemed to include references to deliveries of Shares issued by the Issuer, and Section 2(c)(ii) of such Agreement would not apply.

The Agreement and each Confirmation thereunder will be governed by and construed in accordance with New York law without reference to choice of law doctrine, and each party hereby submits to the jurisdiction of the Courts of the State of New York.

In this Confirmation, "Party A" means Credit Suisse First Boston International, "Party B" means Cephalon, Inc. and "Agent" means Credit Suisse First Boston, acting through its New York branch and solely in its capacity as agent for Party A and Party B.

2.

The terms of the particular Transaction to which this Confirmation relates are as follows:

        General Terms:

Transaction Type:	Convertible Note Hedge. Upon the occurrence of a Conversion Event (as defined below), Party A shall deliver to Party B the number of Shares (as defined below) calculated exclusive of any Make Whole Premium (as defined below) that Party B is obligated to deliver to the holders of the Reference Notes (as defined below) with respect to such Conversion Event.
Trade Date:	December 3, 2004
Settlement Date:	For each Conversion Event, subject to the provisions of Section 6 below, the related Conversion Event Settlement Date.
Seller:	Party A
Buyer:	Party B
Calculation Agent:	Party A, whose determinations and calculations shall be binding in the absence of manifest error. The Calculation Agent will have no responsibility for good faith errors or omissions in making any determination or calculation as provided herein.
Reference Notes:	The Zero Coupon Convertible Subordinated Notes due June 15, 2033 (the "Maturity Date"), first putable on June 15, 2008 and to be issued by Cephalon, Inc. (the "Issuer") on or about December 16, 2004 pursuant to the Note Indenture (as defined below).
Conversion Event:	Each conversion of any Reference Note pursuant to the terms of the Note Indenture (the principal amount of Reference Notes so converted, the "Conversion Amount" with respect to such Conversion Event).
	If the Conversion Amount for any Conversion Event is less than the principal amount of Reference Notes then outstanding, then the terms of this Transaction shall continue to apply, subject to the terms and conditions set forth herein.

2

	Conversion Event Settlement Date:	In respect of each Conversion Event, the date that the Company delivers Shares pursuant to the terms of the Note Indenture to the holders of the Reference Notes so converted (each, an "Indenture Delivery Date"); provided that the Conversion Notice is timely delivered to Party A in accordance with Section 3(d) below and that Party B provides Party A with one Business Day's notice of the Indenture Delivery Date.
	Note Indenture:	The Indenture, to be dated on or about December 16, 2004, between the Issuer and US Bank, National Association, as trustee, as the same may be amended, modified or supplemented and in effect from time to time.
	Shares:	The shares of common stock of the Issuer, par value $0.01 per Share (Bloomberg ticker CEPH, ISIN US1567081096).
	Exchange:	The Nasdaq National Market
	Clearance System:	The Depository Trust Company
Expiration of Convertible Note Hedge:
	Expiration Time:	The close of trading on the Exchange.
	Expiration Date:	June 15, 2008. For the avoidance of doubt this Convertible Note Hedge shall expire on the Expiration Date, with no further payments or deliveries required hereunder (other than payments and deliveries owing hereunder with respect to Conversion Events occurring, and as to which Party A has received notice, on or prior to the Expiration Date), as if this Transaction were an Option Transaction for purposes of the Equity Definitions.
	Automatic Exercise:	Not Applicable.
Settlement upon a Conversion Event:
	Settlement Terms:	Net Share Settlement (as defined below).
	Net Share Settlement:	On each Settlement Date, Party A shall deliver to Party B, through the Agent, the related Share Equivalent Amount.
	Share Equivalent Amount:	With respect to each Conversion Event, the aggregate number of Shares Party B is obligated to deliver to the holders of the Reference Notes that are converted pursuant to such Conversion Event; provided that the Share Equivalent Amount shall exclude any Make Whole Premium (as defined in the Indenture), if any, paid to the holders of the Reference Notes upon such Conversion Event.

3

	Failure to Deliver:	Applicable. For such purposes, Section 6.9 of the Equity Definitions shall apply as if this Transaction were a Physically-settled Transaction, and references in said Section 6.9 to "illiquidity in the market" shall be deemed to include, in addition to "illiquidity in the market", the occurrence of a Disruption Event with respect to the Shares.
	Disruption Event:	A Market Disruption Event as specified in Section 4.3(a)(ii) of the Equity Definitions determined as if this Transaction were a Cash-settled Share Transaction) or a Settlement Disruption Event as specified in Section 6.5 of the Equity Definitions (determined as if this Transaction were a Physically-settled Share Transaction).
Additional Party B Payments:		If a Conversion Event occurs on the Expiration Date, then Party B shall pay to Party A, on the related Settlement Date, an amount (in addition to any related Redemption Equivalent Amount) equal to 0.25% of the related Conversion Amount.
Adjustments:
	Method of Adjustment:	Not applicable.

3.     Additional Agreements, Representations and Covenants of Party B, Etc.:

(a)

Party B hereby represents and warrants to Party A, on each day from the Trade Date to and including the earlier of (i) the date by which Party A is able to initially complete or adjust a hedge of its position created by this Transaction and (ii) the date that is 5 Exchange Business Days following the consummation of the Exchange Offer, that:



(1)

it will not, and will not permit any person or entity subject to its control to, bid for or purchase Shares during such period; and



(2)

Party B has publicly disclosed all material information necessary for Party B to be able to purchase or sell Shares in compliance with applicable federal securities laws and that it has publicly disclosed all material information with respect to its condition (financial or otherwise).



(b)

Party B hereby agrees that, during the Term of this Transaction, it will comply in all material respects with all corporate or, if applicable, similar laws affecting its ability to perform its obligations under this Transaction, including any such requirements of the United States Securities and Exchange Commission (the "Commission") or any applicable law.



(c)

Party B hereby represents and warrants to Party A that (1) Party B has all necessary corporate power and authority to execute, deliver and perform its obligations in respect of this Transaction; such execution, delivery and performance have been duly authorized by all necessary corporate action on Party B's part; and this Confirmation has been duly and validly executed and delivered by Party B and constitutes its legal, valid and binding obligation, enforceable against Party B in accordance with its terms; and (2) neither the execution and delivery of this Confirmation nor the incurrence or performance of obligations of Party B hereunder will conflict with or result in a breach of, or require any consent under, the certificate of incorporation or by-laws (or any equivalent documents) of Party B, or any

4

applicable law or regulation, or any order, writ, injunction or decree of any court or governmental authority or agency, or any agreement or instrument to which Party B or any of its subsidiaries is a party or by which Party B or any of its subsidiaries is bound or to which Party B or any of its subsidiaries is subject, or constitute a default under, or result in the creation of any lien under, any such agreement or instrument.

(d)

The Issuer hereby agrees to promptly deliver to Party A a copy of all notices and other communications required or permitted to be given to the holders of any Reference Notes pursuant to the terms of the Note Indenture on the dates so required or permitted in the Note Indenture. The Issuer further covenants to Party A that it shall provide written notice to Party A, through the Agent, if it receives notice of (i) a conversion with respect to any Reference Notes pursuant to the terms of the Note Indenture (identifying in such notice (a "Conversion Notice") the principal amount of Reference Notes being converted, the CUSIP number of the Reference Notes being converted, the related Conversion Date (as defined in the Indenture) and the date of the commencement of the related Conversion Period (as defined in the Indenture), (ii) a Put Event (including in such notice the principal amount of Reference Notes put in connection therewith), (iii) an Amendment Event (including in such notice a detailed description of any such amendment) or (iv) a Repayment Event (identifying in such notice the nature of such Repayment Event and the principal amount of Reference Notes being paid). The Issuer shall deliver each Conversion Notice to Party A on the related Conversion Date. The Issuer shall deliver notice of a Put Event, Amendment Event or Repayment Event to Party A within two Business Days following the occurrence of any such event. The Issuer hereby acknowledges and agrees that its obligations under this Section 3(d) shall continue as obligations of the Issuer notwithstanding any transfer by it of any of its rights or obligations to any other person or entity in accordance with Section 5 below.



(e)

Notwithstanding anything to the contrary herein, if any event occurs that, pursuant to the terms of the Note Indenture, alters the nature of property that the holders of the Reference Notes will be entitled to receive upon conversion, then the Calculation Agent shall make such adjustments to the terms of this Transaction as it deems necessary to preserve the hedge provided by this Transaction and, in such connection, the Calculation Agent may adjust (1) the definition of "Shares" herein to reflect the property into which the Reference Notes are convertible after giving effect to such event, and (2) Party A's obligations to deliver Shares (or to pay amounts determined by reference to the value of Shares) hereunder so that Party A will instead be obligated to deliver such property (or to pay the equivalent value thereof as reasonably determined by the Calculation Agent).



(f)

Notwithstanding anything herein to the contrary, Party A and Party B agree that the Original Confirmation shall continue in full force and effect (in the form originally executed on June 6, 2003 (as such form may be amended)), to the extent that any Original Notes remain outstanding following the Exchange Offer. In addition, Party A and Party B agree that the Exchange Offer shall not constitute a Repayment Event or Additional Termination Event under and as defined in the Original Confirmation.

4.     Additional Termination Events:

        The occurrence of any the following shall be an Additional Termination Event with respect to Party B (which shall be the sole Affected Party and this Transaction shall be the sole Affected Transaction):

(a)

an Amendment Event occurs, in which case the entirety of this Transaction shall be subject to termination; or

5

(b)

a Repayment Event occurs, in which case this Transaction shall be subject to termination only in respect of the principal amount of Reference Notes that cease to be outstanding in connection with or as a result of such Repayment Event (and, for the avoidance of doubt, if the principal amount of Reference Notes that cease to be outstanding is less than the total principal amount outstanding of Reference Notes, then the terms of this Transaction shall continue to apply, subject to the terms and conditions set forth herein).

        In addition:

(x)

if the Exchange Offer is not consummated then the entirety of this Transaction shall terminate automatically, no payments or deliveries shall be required hereunder and the Original Confirmation shall continue in full force and effect; and



(y)

if a Put Event occurs, then this Transaction shall terminate automatically in respect of the principal amount of Reference Notes that cease to be outstanding in connection with or as a result of such Put Event and no payments or deliveries shall be required hereunder in respect of such Put Event (and, for the avoidance of doubt, if the principal amount of Reference Notes that cease to be outstanding is less than the total principal amount outstanding of Reference Notes, then the terms of this Transaction shall continue to apply, subject to the terms and conditions set forth herein).

        As used in this Section 4:

        "Amendment Event" means that the Issuer amends, modifies, supplements or waives any term of the Note Indenture or the Reference Notes if such amendment, modification, supplement or waiver has a material effect on this Transaction or Party A's ability to hedge all or a portion of this Transaction, with such materiality determination to be made in the sole discretion of the Calculation Agent.

        "Put Event" means the put of any Reference Notes to the Issuer by the holder thereof pursuant to the terms of the Note Indenture (other than any put in connection with a change of control or other similar corporate transaction).

        "Repayment Event" means that (a) any Reference Notes are repurchased or redeemed (in each case whether in connection with or as a result of a change of control, howsoever defined, or for any other reason) by the Issuer, (b) any Reference Notes are delivered to the Issuer in exchange for delivery of any property or assets of the Issuer or any of its affiliates (howsoever described), (c) any principal of any of the Reference Notes is repaid prior to the Maturity Date (whether following acceleration of the Reference Notes or otherwise), or (d) any Reference Notes are exchanged by or for the benefit of the holders thereof for any other securities of the Issuer or any of its affiliates (or any other property, or any combination thereof) pursuant to any exchange offer or similar transaction, provided that Put Events shall not constitute Repayment Events.

5.     Transfer:

(a)

Notwithstanding Section 7 of the Agreement, Party A may transfer its rights and obligations under this Transaction:



(1)

without the consent of Party B to any person or entity, provided (x) that the rating by Moody's Investors Service Inc. or Standard and Poor's Ratings Services of the long-term, senior unsecured indebtedness of the transferee (or any Credit Support Provider for such transferee) shall be at least equal to the rating by such rating agency of the long-term, senior unsecured indebtedness of Party A as at the date of such transfer and (y) in Party B's reasonable judgment, such transfer will not have a material adverse tax consequence on Party B; or

6

(2)

to any other person or entity with Party B's consent (such consent not to be unreasonably withheld),

in each case subject to any applicable federal or state laws, regulations or other requirements.

(b)

Notwithstanding Section 7 of the Agreement, Party B may transfer its rights and obligations (other than, if Party B is the Issuer, those under Section 3(d) above) under this Transaction with the consent of Party A (such consent not to be unreasonably withheld), subject to any applicable federal or state laws, regulations or other requirements, and subject in all cases to Party A's standard compliance processes.

6.     Staggered Settlement:

        If Party A determines reasonably and in good faith that the number of Shares required to be delivered to Party B hereunder on any Settlement Date would exceed 9.9% of all outstanding Shares, then Party A may, by notice to Party B on or prior to such Settlement Date (a "Nominal Settlement Date"), elect to deliver the Shares comprising the related Share Equivalent Amount on two or more dates (each, a "Staggered Settlement Date") as follows:

(a)

in such notice, Party A will specify to Party B the related Staggered Settlement Dates (the first of which will be such Nominal Settlement Date and the last of which will be no later than the twentieth (20th) Exchange Business Day following such Nominal Settlement Date; provided that Party A shall use its commercially reasonable efforts to deliver all of such Shares as soon as possible following such Nominal Settlement Date) and the number of Shares that it will deliver on each Staggered Settlement Date;



(b)

the aggregate number of Shares that Party A will deliver to Party B hereunder on all such Staggered Settlement Dates will equal the number of Shares that Party A would otherwise be required to deliver on such Nominal Settlement Date; and



(c)

the Net Share Settlement terms set forth above will apply on each Staggered Settlement Date, except that the Shares comprising the Share Equivalent Amount will be allocated among such Staggered Settlement Dates as specified by Party A in the notice referred to in clause (a) above.

        Notwithstanding anything herein to the contrary, Party A shall be entitled to deliver Shares to Party B from time to time prior to the date on which Party A would be obligated to deliver them to Party B pursuant to the Net Share Settlement terms set forth above, and Party B agrees to credit all such early deliveries against Party A's obligations hereunder in the direct order in which such obligations arise. No such early delivery of Shares will accelerate or otherwise affect any of Party B's obligations to Party A hereunder. To the extent Party A receives or is entitled to receive any distribution or payment in respect of Shares by reason of Party A's being a holder of record of such Shares on any date after the Nominal Settlement Date which Party A would have delivered to Party B on such Nominal Settlement Date but for the provisions of this Section 6, Party A shall deliver such distribution or payment to Party B at the time Party A delivers the related Shares to Party B in accordance with this Section 6, if such distribution or payment has already been received by Party A at such time, or within a reasonable period of time following Party A's receipt of the distribution or payment, if such distribution or payment has not already been received by Party A at the time Party A delivers the related Shares to Party B in accordance with this Section 6.

7.     Matters relating to the Agent:

(a)

Credit Suisse First Boston, New York branch, in its capacity as Agent will be responsible for (i) effecting this Transaction, (ii) issuing all required confirmations and statements to Party A and Party B, (iii) maintaining books and records relating to this Transaction in accordance

7

with its standard practices and procedures and in accordance with applicable law and (iv) unless otherwise requested by Party B, receiving, delivering, and safeguarding Party B's funds and any securities in connection with this Transaction, in accordance with its standard practices and procedures and in accordance with applicable law.

(b)

Agent is acting in connection with this Transaction solely in its capacity as Agent for Party A and Party B pursuant to instructions from Party A and Party B. Agent shall have no responsibility or personal liability to Party A or Party B arising from any failure by Party A or Party B to pay or perform any obligations hereunder, or to monitor or enforce compliance by Party A or Party B with any obligation hereunder, including, without limitation, any obligations to maintain collateral. Each of Party A and Party B agrees to proceed solely against the other to collect or recover any securities or monies owing to it in connection with or as a result of this Transaction. Agent shall otherwise have no liability in respect of this Transaction, except for its gross negligence or willful misconduct in performing its duties as Agent.



(c)

Any and all notices, demands, or communications of any kind relating to this Transaction between Party A and Party B shall be transmitted exclusively through Agent at the following address:

Credit Suisse First Boston, New York branch
Eleven Madison Avenue
New York, NY 10010-3629

For payments and deliveries:
Facsimile No.: (212) 325 8175
Telephone No.: (212) 325 8678 / (212) 325 3213

For all other communications:
Facsimile No.: (212) 325 8173
Telephone No.: (212) 325 8676 / (212) 538 5306 /
(212) 538 1193 / (212) 538 6886

(d)

The date and time of the Transaction evidenced hereby will be furnished by the Agent to Party A and Party B upon written request.



(e)

The Agent will furnish to Party B upon written request a statement as to the source and amount of any remuneration received or to be received by the Agent in connection with the Transaction evidenced hereby.



(f)

Party A and Party B each represents and agrees (i) that this Transaction is not unsuitable for it in the light of such party's financial situation, investment objectives and needs and (ii) that it is entering into this Transaction in reliance upon such tax, accounting, regulatory, legal and financial advice as it deems necessary and not upon any view expressed by the other or the Agent.

8.     Account Details:

Payments to Agent:	The Bank of New York Swift:    IRVTUS3N A/C:    Credit Suisse First Boston A/C#:    8900374179
Payments to Party A:	To be advised
Payments to Party B:	To be advised
Deliveries to Party B:	To be advised

        Credit Suisse First Boston International is regulated by The Financial Services Authority and has entered into this Transaction as principal. The time at which this Transaction was executed will be notified to Party B (through the Agent) on request.

8

        Please confirm that the foregoing correctly sets forth the terms of your agreement by signing and returning this Confirmation.

		Yours faithfully,
		CREDIT SUISSE FIRST BOSTON, acting through its New York branch and solely in its capacity as Agent
		By:	/s/  LEONARD BOUCHARD Name: Leonard Bouchard Title:  Vice President Operations
		By:	/s/  JOHN RYAN Name: John Ryan Title:  A.V.P. Operations
Confirmed as of the date first written above:
CEPHALON, INC. (Party B)
By:	/s/  FRANK BALDINO, JR. Name: Frank Baldino, Jr. Title:  Chairman and CEO
CREDIT SUISSE FIRST BOSTON INTERNATIONAL (Party A)
By:	/s/  MARK SKINNER Name: Mark Skinner Title:  Vice President
By:	/s/  ANITA KHOSLA Name: Anita Khosla Title:  Vice President

9

EX-99.(D)(6)

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 99(d)(6)

CONVERTIBLE NOTE HEDGE
(SEVEN YEAR)

December 3, 2004

Cephalon, Inc.
145 Brandywine Parkway
West Chester, PA 19380
Attention: Kevin Buchi, Senior Vice President &
        Chief Financial Officer

Credit Suisse First Boston International
One Cabot Square
London E14 4QJ
England

Dear Sirs:

        In connection with the exchange offer (the "Exchange Offer") expected to be consummated on or about December 16, 2004 of the Issuer's (as defined below) Zero Coupon Convertible Subordinated Notes due June 15, 2033, first putable on June 15, 2010, issued on June 11, 2003 with an original principal amount of $375,000,000 (the "Original Notes"), with the Reference Notes described below, Party A and Party B hereby agree that this letter agreement (this "Confirmation") shall supersede and replace, except to the extent expressly stated below, the confirmation for the Convertible Note Hedge (Seven Year), dated June 6, 2003, Reference Number 40046261 (the "Original Confirmation"), between Party A and Party B. This Confirmation constitutes a "Confirmation" as referred to in the Agreement specified below.

1.

The definitions and provisions contained in the 1996 ISDA Equity Derivatives Definitions (the "Equity Definitions") and in the 2000 ISDA Definitions (the "Swap Definitions" and, together with the Equity Definitions, the "Definitions") (in each case as published by the International Swaps and Derivatives Association, Inc.) are incorporated into this Confirmation. In the event of any inconsistency between the Equity Definitions and the Swap Definitions, the Equity Definitions will govern, and between the Definitions and this Confirmation, this Confirmation will prevail. References herein to a "Transaction" shall be deemed to be references to a "Share Option Transaction" for purposes of the Equity Definitions and an "Swap Transaction" for the purposes of the Swap Definitions.

This Transaction (this "Transaction") together with all other Confirmations of Share Transactions between Party A and Party B with respect to Shares of the Issuer contemporaneously or previously entered into between them, notwithstanding anything to the contrary therein, shall supplement, form a part of, and be subject to an ISDA 1992 Master Agreement (Multicurrency—Cross Border) (the "Agreement"), as if, on the Trade Date of the first such Transaction between Party A and Party B, they had executed the Agreement (without any Schedule thereto) and specified that (1) the Automatic Early Termination provisions contained in Section 6(a) of such Agreement would apply, (2) Second Method and Loss would apply, (3) such Agreement would cover only Share Transactions with respect to Shares of the Issuer referred to herein and (4) for purposes of Section 2(c) of such Agreement, references to payments of amounts denominated in the same currency shall be deemed to include references to deliveries of Shares issued by the Issuer, and Section 2(c)(ii) of such Agreement would not apply.

The Agreement and each Confirmation thereunder will be governed by and construed in accordance with New York law without reference to choice of law doctrine, and each party hereby submits to the jurisdiction of the Courts of the State of New York.

In this Confirmation, "Party A" means Credit Suisse First Boston International, "Party B" means Cephalon, Inc. and "Agent" means Credit Suisse First Boston, acting through its New York branch and solely in its capacity as agent for Party A and Party B.

2.

The terms of the particular Transaction to which this Confirmation relates are as follows:

        General Terms:

Transaction Type:	Convertible Note Hedge. Upon the occurrence of a Conversion Event (as defined below), Party A shall deliver to Party B the number of Shares (as defined below) calculated exclusive of any Make Whole Premium (as defined below) that Party B is obligated to deliver to the holders of the Reference Notes (as defined below) with respect to such Conversion Event.
Trade Date:	December 3, 2004
Settlement Date:	For each Conversion Event, subject to the provisions of Section 6 below, the related Conversion Event Settlement Date.
Seller:	Party A
Buyer:	Party B
Calculation Agent:	Party A, whose determinations and calculations shall be binding in the absence of manifest error. The Calculation Agent will have no responsibility for good faith errors or omissions in making any determination or calculation as provided herein.
Reference Notes:	The Zero Coupon Convertible Subordinated Notes due June 15, 2033 (the "Maturity Date"), first putable on June 15, 2010 and to be issued by Cephalon, Inc. (the "Issuer") on or about December 16, 2004 pursuant to the Note Indenture (as defined below).
Conversion Event:	Each conversion of any Reference Note pursuant to the terms of the Note Indenture (the principal amount of Reference Notes so converted, the "Conversion Amount" with respect to such Conversion Event).
	If the Conversion Amount for any Conversion Event is less than the principal amount of Reference Notes then outstanding, then the terms of this Transaction shall continue to apply, subject to the terms and conditions set forth herein.

2

	Conversion Event Settlement Date:	In respect of each Conversion Event, the date that the Company delivers Shares pursuant to the terms of the Note Indenture to the holders of the Reference Notes so converted (each, an "Indenture Delivery Date"); provided that the Conversion Notice is timely delivered to Party A in accordance with Section 3(d) below and that Party B provides Party A with one Business Day's notice of the Indenture Delivery Date.
	Note Indenture:	The Indenture, to be dated on or about December 16, 2004, between the Issuer and US Bank, National Association, as trustee, as the same may be amended, modified or supplemented and in effect from time to time.
	Shares:	The shares of common stock of the Issuer, par value $0.01 per Share (Bloomberg ticker CEPH, ISIN US1567081096).
	Exchange:	The Nasdaq National Market
	Clearance System:	The Depository Trust Company
Expiration of Convertible Note Hedge:
	Expiration Time:	The close of trading on the Exchange.
	Expiration Date:	June 15, 2010. For the avoidance of doubt this Convertible Note Hedge shall expire on the Expiration Date, with no further payments or deliveries required hereunder (other than payments and deliveries owing hereunder with respect to Conversion Events occurring, and as to which Party A has received notice, on or prior to the Expiration Date), as if this Transaction were an Option Transaction for purposes of the Equity Definitions.
	Automatic Exercise:	Not Applicable.
Settlement upon a Conversion Event:
	Settlement Terms:	Net Share Settlement (as defined below).
	Net Share Settlement:	On each Settlement Date, Party A shall deliver to Party B, through the Agent, the related Share Equivalent Amount.
	Share Equivalent Amount:	With respect to each Conversion Event, the aggregate number of Shares Party B is obligated to deliver to the holders of the Reference Notes that are converted pursuant to such Conversion Event; provided that the Share Equivalent Amount shall exclude any Make Whole Premium (as defined in the Indenture), if any, paid to the holders of the Reference Notes upon such Conversion Event.

3

	Failure to Deliver:	Applicable. For such purposes, Section 6.9 of the Equity Definitions shall apply as if this Transaction were a Physically-settled Transaction, and references in said Section 6.9 to "illiquidity in the market" shall be deemed to include, in addition to "illiquidity in the market", the occurrence of a Disruption Event with respect to the Shares.
	Disruption Event:	A Market Disruption Event as specified in Section 4.3(a)(ii) of the Equity Definitions (determined as if this Transaction were a Cash-settled Share Transaction) or a Settlement Disruption Event as specified in Section 6.5 of the Equity Definitions (determined as if this Transaction were a Physically-settled Share Transaction).
Additional Party B Payments:		If a Conversion Event occurs on the Expiration Date, then Party B shall pay to Party A, on the related Settlement Date, an amount (in addition to any related Redemption Equivalent Amount) equal to 0.25% of the related Conversion Amount.
Adjustments:
	Method of Adjustment:	Not applicable.

3.     Additional Agreements, Representations and Covenants of Party B, Etc.:

(a)

Party B hereby represents and warrants to Party A, on each day from the Trade Date to and including the earlier of (i) the date by which Party A is able to initially complete or adjust a hedge of its position created by this Transaction and (ii) the date that is 5 Exchange Business Days following the consummation of the Exchange Offer, that:



(1)

it will not, and will not permit any person or entity subject to its control to, bid for or purchase Shares during such period; and



(2)

Party B has publicly disclosed all material information necessary for Party B to be able to purchase or sell Shares in compliance with applicable federal securities laws and that it has publicly disclosed all material information with respect to its condition (financial or otherwise).



(b)

Party B hereby agrees that, during the Term of this Transaction, it will comply in all material respects with all corporate or, if applicable, similar laws affecting its ability to perform its obligations under this Transaction, including any such requirements of the United States Securities and Exchange Commission (the "Commission") or any applicable law.



(c)

Party B hereby represents and warrants to Party A that (1) Party B has all necessary corporate power and authority to execute, deliver and perform its obligations in respect of this Transaction; such execution, delivery and performance have been duly authorized by all necessary corporate action on Party B's part; and this Confirmation has been duly and validly executed and delivered by Party B and constitutes its legal, valid and binding obligation, enforceable against Party B in accordance with its terms; and (2) neither the execution and delivery of this Confirmation nor the incurrence or performance of obligations of Party B hereunder will conflict with or result in a breach of, or require any consent under, the certificate of incorporation or by-laws (or any equivalent documents) of Party B, or any

4

applicable law or regulation, or any order, writ, injunction or decree of any court or governmental authority or agency, or any agreement or instrument to which Party B or any of its subsidiaries is a party or by which Party B or any of its subsidiaries is bound or to which Party B or any of its subsidiaries is subject, or constitute a default under, or result in the creation of any lien under, any such agreement or instrument.

(d)

The Issuer hereby agrees to promptly deliver to Party A a copy of all notices and other communications required or permitted to be given to the holders of any Reference Notes pursuant to the terms of the Note Indenture on the dates so required or permitted in the Note Indenture. The Issuer further covenants to Party A that it shall provide written notice to Party A, through the Agent, if it receives notice of (i) a conversion with respect to any Reference Notes pursuant to the terms of the Note Indenture (identifying in such notice (a "Conversion Notice") the principal amount of Reference Notes being converted, the CUSIP number of the Reference Notes being converted, the related Conversion Date (as defined in the Indenture) and the date of the commencement of the related Conversion Period (as defined in the Indenture), (ii) a Put Event (including in such notice the principal amount of Reference Notes put in connection therewith), (iii) an Amendment Event (including in such notice a detailed description of any such amendment) or (iv) a Repayment Event (identifying in such notice the nature of such Repayment Event and the principal amount of Reference Notes being paid). The Issuer shall deliver each Conversion Notice to Party A on the related Conversion Date. The Issuer shall deliver notice of a Put Event, Amendment Event or Repayment Event to Party A within two Business Days following the occurrence of any such event. The Issuer hereby acknowledges and agrees that its obligations under this Section 3(d) shall continue as obligations of the Issuer notwithstanding any transfer by it of any of its rights or obligations to any other person or entity in accordance with Section 5 below.



(e)

Notwithstanding anything to the contrary herein, if any event occurs that, pursuant to the terms of the Note Indenture, alters the nature of property that the holders of the Reference Notes will be entitled to receive upon conversion, then the Calculation Agent shall make such adjustments to the terms of this Transaction as it deems necessary to preserve the hedge provided by this Transaction and, in such connection, the Calculation Agent may adjust (1) the definition of "Shares" herein to reflect the property into which the Reference Notes are convertible after giving effect to such event, and (2) Party A's obligations to deliver Shares (or to pay amounts determined by reference to the value of Shares) hereunder so that Party A will instead be obligated to deliver such property (or to pay the equivalent value thereof as reasonably determined by the Calculation Agent).



(f)

Notwithstanding anything herein to the contrary, Party A and Party B agree that the Original Confirmation shall continue in full force and effect (in the form originally executed on June 6, 2003 (as such form may be amended)), to the extent that any Original Notes remain outstanding following the Exchange Offer. In addition, Party A and Party B agree that the Exchange Offer shall not constitute a Repayment Event or Additional Termination Event under and as defined in the Original Confirmation.

4.     Additional Termination Events:

        The occurrence of any the following shall be an Additional Termination Event with respect to Party B (which shall be the sole Affected Party and this Transaction shall be the sole Affected Transaction):

(a)

an Amendment Event occurs, in which case the entirety of this Transaction shall be subject to termination; or

5

(b)

a Repayment Event occurs, in which case this Transaction shall be subject to termination only in respect of the principal amount of Reference Notes that cease to be outstanding in connection with or as a result of such Repayment Event (and, for the avoidance of doubt, if the principal amount of Reference Notes that cease to be outstanding is less than the total principal amount outstanding of Reference Notes, then the terms of this Transaction shall continue to apply, subject to the terms and conditions set forth herein).

        In addition:

(x)

if the Exchange Offer is not consummated then the entirety of this Transaction shall terminate automatically, no payments or deliveries shall be required hereunder and the Original Confirmation shall continue in full force and effect; and



(y)

if a Put Event occurs, then this Transaction shall terminate automatically in respect of the principal amount of Reference Notes that cease to be outstanding in connection with or as a result of such Put Event and no payments or deliveries shall be required hereunder in respect of such Put Event (and, for the avoidance of doubt, if the principal amount of Reference Notes that cease to be outstanding is less than the total principal amount outstanding of Reference Notes, then the terms of this Transaction shall continue to apply, subject to the terms and conditions set forth herein).

        As used in this Section 4:

        "Amendment Event" means that the Issuer amends, modifies, supplements or waives any term of the Note Indenture or the Reference Notes if such amendment, modification, supplement or waiver has a material effect on this Transaction or Party A's ability to hedge all or a portion of this Transaction, with such materiality determination to be made in the sole discretion of the Calculation Agent.

        "Put Event" means the put of any Reference Notes to the Issuer by the holder thereof pursuant to the terms of the Note Indenture (other than any put in connection with a change of control or other similar corporate transaction).

        "Repayment Event" means that (a) any Reference Notes are repurchased or redeemed (in each case whether in connection with or as a result of a change of control, howsoever defined, or for any other reason) by the Issuer, (b) any Reference Notes are delivered to the Issuer in exchange for delivery of any property or assets of the Issuer or any of its affiliates (howsoever described), (c) any principal of any of the Reference Notes is repaid prior to the Maturity Date (whether following acceleration of the Reference Notes or otherwise), or (d) any Reference Notes are exchanged by or for the benefit of the holders thereof for any other securities of the Issuer or any of its affiliates (or any other property, or any combination thereof) pursuant to any exchange offer or similar transaction, provided that Put Events shall not constitute Repayment Events.

5.     Transfer:

(a)

Notwithstanding Section 7 of the Agreement, Party A may transfer its rights and obligations under this Transaction:



(1)

without the consent of Party B to any person or entity, provided (x) that the rating by Moody's Investors Service Inc. or Standard and Poor's Ratings Services of the long-term, senior unsecured indebtedness of the transferee (or any Credit Support Provider for such transferee) shall be at least equal to the rating by such rating agency of the long-term, senior unsecured indebtedness of Party A as at the date of such transfer and (y) in Party B's reasonable judgment, such transfer will not have a material adverse tax consequence on Party B; or

6

(2)

to any other person or entity with Party B's consent (such consent not to be unreasonably withheld),

        in each case subject to any applicable federal or state laws, regulations or other requirements.

(b)

Notwithstanding Section 7 of the Agreement, Party B may transfer its rights and obligations (other than, if Party B is the Issuer, those under Section 3(d) above) under this Transaction with the consent of Party A (such consent not to be unreasonably withheld), subject to any applicable federal or state laws, regulations or other requirements, and subject in all cases to Party A's standard compliance processes.

6.     Staggered Settlement:

        If Party A determines reasonably and in good faith that the number of Shares required to be delivered to Party B hereunder on any Settlement Date would exceed 9.9% of all outstanding Shares, then Party A may, by notice to Party B on or prior to such Settlement Date (a "Nominal Settlement Date"), elect to deliver the Shares comprising the related Share Equivalent Amount on two or more dates (each, a "Staggered Settlement Date") as follows:

(a)

in such notice, Party A will specify to Party B the related Staggered Settlement Dates (the first of which will be such Nominal Settlement Date and the last of which will be no later than the twentieth (20th) Exchange Business Day following such Nominal Settlement Date; provided that Party A shall use its commercially reasonable efforts to deliver all of such Shares as soon as possible following such Nominal Settlement Date) and the number of Shares that it will deliver on each Staggered Settlement Date;



(b)

the aggregate number of Shares that Party A will deliver to Party B hereunder on all such Staggered Settlement Dates will equal the number of Shares that Party A would otherwise be required to deliver on such Nominal Settlement Date; and



(c)

the Net Share Settlement terms set forth above will apply on each Staggered Settlement Date, except that the Shares comprising the Share Equivalent Amount will be allocated among such Staggered Settlement Dates as specified by Party A in the notice referred to in clause (a) above.

        Notwithstanding anything herein to the contrary, Party A shall be entitled to deliver Shares to Party B from time to time prior to the date on which Party A would be obligated to deliver them to Party B pursuant to the Net Share Settlement terms set forth above, and Party B agrees to credit all such early deliveries against Party A's obligations hereunder in the direct order in which such obligations arise. No such early delivery of Shares will accelerate or otherwise affect any of Party B's obligations to Party A hereunder. To the extent Party A receives or is entitled to receive any distribution or payment in respect of Shares by reason of Party A's being a holder of record of such Shares on any date after the Nominal Settlement Date which Party A would have delivered to Party B on such Nominal Settlement Date but for the provisions of this Section 6, Party A shall deliver such distribution or payment to Party B at the time Party A delivers the related Shares to Party B in accordance with this Section 6, if such distribution or payment has already been received by Party A at such time, or within a reasonable period of time following Party A's receipt of the distribution or payment, if such distribution or payment has not already been received by Party A at the time Party A delivers the related Shares to Party B in accordance with this Section 6.

7.     Matters relating to the Agent:

(a)

Credit Suisse First Boston, New York branch, in its capacity as Agent will be responsible for (i) effecting this Transaction, (ii) issuing all required confirmations and statements to Party A and Party B, (iii) maintaining books and records relating to this Transaction in accordance

7

with its standard practices and procedures and in accordance with applicable law and (iv) unless otherwise requested by Party B, receiving, delivering, and safeguarding Party B's funds and any securities in connection with this Transaction, in accordance with its standard practices and procedures and in accordance with applicable law.

(b)

Agent is acting in connection with this Transaction solely in its capacity as Agent for Party A and Party B pursuant to instructions from Party A and Party B. Agent shall have no responsibility or personal liability to Party A or Party B arising from any failure by Party A or Party B to pay or perform any obligations hereunder, or to monitor or enforce compliance by Party A or Party B with any obligation hereunder, including, without limitation, any obligations to maintain collateral. Each of Party A and Party B agrees to proceed solely against the other to collect or recover any securities or monies owing to it in connection with or as a result of this Transaction. Agent shall otherwise have no liability in respect of this Transaction, except for its gross negligence or willful misconduct in performing its duties as Agent.



(c)

Any and all notices, demands, or communications of any kind relating to this Transaction between Party A and Party B shall be transmitted exclusively through Agent at the following address:

Credit Suisse First Boston, New York branch
Eleven Madison Avenue
New York, NY 10010-3629

For payments and deliveries:
Facsimile No.: (212) 325 8175
Telephone No.: (212) 325 8678 / (212) 325 3213

For all other communications:
Facsimile No.: (212) 325 8173
Telephone No.: (212) 325 8676 / (212) 538 5306 /
(212) 538 1193 / (212) 538 6886

(d)

The date and time of the Transaction evidenced hereby will be furnished by the Agent to Party A and Party B upon written request.



(e)

The Agent will furnish to Party B upon written request a statement as to the source and amount of any remuneration received or to be received by the Agent in connection with the Transaction evidenced hereby.



(f)

Party A and Party B each represents and agrees (i) that this Transaction is not unsuitable for it in the light of such party's financial situation, investment objectives and needs and (ii) that it is entering into this Transaction in reliance upon such tax, accounting, regulatory, legal and financial advice as it deems necessary and not upon any view expressed by the other or the Agent.

8.     Account Details:

Payments to Agent:	The Bank of New York Swift:    IRVTUS3N A/C:    Credit Suisse First Boston A/C#:    8900374179
Payments to Party A:	To be advised
Payments to Party B:	To be advised
Deliveries to Party B:	To be advised

        Credit Suisse First Boston International is regulated by The Financial Services Authority and has entered into this Transaction as principal. The time at which this Transaction was executed will be notified to Party B (through the Agent) on request.

8

        Please confirm that the foregoing correctly sets forth the terms of your agreement by signing and returning this Confirmation.

		Yours faithfully,
		CREDIT SUISSE FIRST BOSTON, acting through its New York branch and solely in its capacity as Agent
		By:	/s/  CHRISTY GRANT Name: Christy Grant Title:  Assistant Vice President Operations
		By:	/s/  SPENCER SMITH Name: Spencer Smith Title:  Assistant Vice President Operations
Confirmed as of the date first written above:
CEPHALON, INC. (Party B)
By:	/s/  FRANK BALDINO, JR. Name: Frank Baldino, Jr. Title:  Chairman and CEO
CREDIT SUISSE FIRST BOSTON INTERNATIONAL (Party A)
By:	/s/  MARK SKINNER Name: Mark Skinner Title:  Vice President
By:	/s/  ANITA KHOSLA Name: Anita Khosla Title:    Vice President

9

QuickLinks

Credit Suisse First Boston, New York branch Eleven Madison Avenue New York, NY 10010-3629 For payments and deliveries: Facsimile No.: (212) 325 8175 Telephone No.: (212) 325 8678 / (212) 325 3213 For all other communications: Facsimile No.: (212) 325 8173 Telephone No.: (212) 325 8676 / (212) 538 5306 / (212) 538 1193 / (212) 538 6886

CORRESP

QuickLinks -- Click here to rapidly navigate through this document

[LETTERHEAD OF SIDLEY AUSTIN BROWN & WOOD LLP]

December 13, 2004

VIA EDGAR SUBMISSION

Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C. 20549
Attention:        Ms. Julia E. Griffith

Re:

Cephalon, Inc.
Schedule TO, filed November 16, 2004
SEC File No. 005-41753

Ladies and Gentlemen:

        On behalf of Cephalon, Inc. (the "Company"), we are writing in response to the comments contained in the staff's comment letter dated December 9, 2004 (the "Comment Letter") with respect to the Company's Tender Offer Statement on Form TO, as filed with the SEC on November 16, 2004 (the "Schedule TO"). On the date hereof, the Company has filed Amendment No. 1 to its Schedule TO ("Amendment No. 1"). For the convenience of the staff's review, we have set forth the comments contained in the Comment Letter along with the responses of the Company.

Offer to Exchange Cover Page

1.

Please revise your disclosure to include the date that the old notes were issued.

RESPONSE: The Company has revised its disclosure as requested.

Summary Financial Information, page 2

2.

Revise your disclosure to include the earnings per share information required by Item 1010(b)(2) of Regulation M-A.

RESPONSE: Information required by Item 1010(b)(2) of Regulation M-A has not been included because the Company has informed us that it has determined that any pro forma effect of the exchange offer on earnings per share would not be material.

Special Note Regarding Forward-Looking Statements, page 20

3.

On page 21 you state that you will not update forward-looking statement "except as required by law." Please revise this disclosure to clarify your obligation under Rules 13e-4(d)(2) to amend the document to reflect a material change in the information previously disclosed.

RESPONSE: The Company has revised its disclosure as requested.

The Exchange Offer, page 23
Conditions to the Exchange Offer, page 26

4.

We note that you may waive the conditions you list in your document at any time in your sole discretion. Please confirm your understanding that if you waive a material condition, the offer must remain open for at least five business days after that waiver.

RESPONSE: The Company hereby confirms its understanding that if it waives a material condition, the offer must remain open for at least five business days after that waiver.

1

Exchange Agent, page 30

5.

You state that the exchange agent will be paid "customary compensation for its services...." Revise to provide the information required by Item 1009(a) of Regulation M-A.

RESPONSE: The Company has revised its disclosure as requested.

Where You can Find More Information, page 67

6.

Schedule TO does not specifically allow you to forward incorporate disclosure in subsequently filed documents. In fact, doing so is inconsistent with the technical requirements of General Instruction F of Schedule TO and your obligation under Rules 13e-4(c)(3) and 13e-4(e)(3) to amend the Schedule to reflect a material change in the information previously disclosed. Please revise.

RESPONSE: The Company has revised its disclosure to clarify that it is not forward incorporating disclosure in subsequently filed documents.

        In addition, in response to your Comment Letter, the Company has advised us as follows:

•

the Company acknowledges that it is responsible for the adequacy and accuracy of the disclosure in the Schedule TO;



•

staff comments or changes to disclosure in response to staff comments in the Schedule TO do not foreclose the Commission from taking any action with respect to the Schedule TO; and



•

the Company acknowledges that the Company may not assert staff comments as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

* * * * *

        If you have any questions regarding the foregoing or Amendment No. 1, please contact the undersigned at (312) 853-4161 or John M. Limongelli of the Company at (610) 738-6515.

Very truly yours,

/s/  PRAN JHA

Pran Jha

cc:

John M. Limongelli

2

QuickLinks

[LETTERHEAD OF SIDLEY AUSTIN BROWN & WOOD LLP]