UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE TO

(RULE 14D-100)

Tender Offer Statement Pursuant to Section 14(d)(1) or 13(e)(1)

of the Securities Exchange Act of 1934

(Amendment No. 5)

ARIAD Pharmaceuticals, Inc.

(Name of Subject Company)

KIKU MERGER CO., INC.

(Offeror)

TAKEDA PHARMACEUTICAL COMPANY LIMITED

(Parent of Offeror)

(Names of Filing Persons)

Common stock, par value $0.001 per share

(Title of Class of Securities)

04033A100

(CUSIP Number of Class of Securities)

James Kehoe

Takeda Pharmaceutical Company Limited

12-10, Nihonbashi 2-chome, Chuo-ku, Tokyo 103-8668

Tel: +81 3 3278-2111

(Name, Address and Telephone Number of Person Authorized to Receive Notices and

Communications on Behalf of Filing Persons)

With a copy to:

Paul J. Shim

Kimberly R. Spoerri

Cleary Gottlieb Steen & Hamilton LLP

One Liberty Plaza

New York, New York 10006

(212) 225-2000

CALCULATION OF FILING FEE

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

Check the following box if the filing is a final amendment reporting the results of the tender offer:  ☒

This Amendment No. 5 (this “Amendment”) amends and supplements the Tender Offer Statement on Schedule TO filed by Kiku Merger Co., Inc., a Delaware corporation (“Purchaser”) and a wholly-owned indirect subsidiary of Takeda Pharmaceutical Company Limited, a corporation organized under the laws of Japan (“Takeda”), with the Securities and Exchange Commission on January 19, 2017 (together with any subsequent amendments and supplements thereto, including this Amendment, the “Schedule TO”). The Schedule TO relates to the tender offer by Purchaser for all of the outstanding shares of common stock, par value $0.001 per share (“Shares”), of ARIAD Pharmaceuticals, Inc., a Delaware corporation (“ARIAD”), at a price of $24.00 per Share in cash, net of applicable withholding taxes and without interest, upon the terms and subject to the conditions set forth in the Offer to Purchase, dated January 19, 2017 (the “Offer to Purchase”), a copy of which is attached as Exhibit (a)(1)(A), and in the related letter of transmittal (the “Letter of Transmittal”, a copy of which is attached as Exhibit (a)(1)(B), and which, together with the Offer to Purchase and other related materials, as each may be amended or supplemented from time to time, collectively constitute the “Offer”).

All the information set forth in the Offer to Purchase, including Schedule I thereto, is incorporated by reference herein in response to Items 1 through 9 and Item 11 of this Schedule TO, and is supplemented by the information specifically provided in this Amendment.

Capitalized terms used but not defined in this Amendment shall have the meanings assigned to such terms in the Schedule TO.

Items 1 through 9 and Item 11.

The Offer to Purchase and Items 1 through 9 and Item 11 of the Schedule TO, to the extent such Items incorporate by reference the information contained in the Offer to Purchase, are hereby amended and supplemented as set forth below:

“The Offer and withdrawal rights expired as scheduled at 11:59 p.m., Eastern time, on Wednesday, February 15, 2017. The Depositary has indicated that, as of the Expiration Time, a total of 158,558,628 Shares (excluding Shares with respect to which notices of guaranteed delivery were delivered but which Shares were not yet delivered) have been validly tendered and not validly withdrawn pursuant to the Offer, representing approximately 81.4% of the outstanding Shares as of the Expiration Time. The number of Shares validly tendered and not properly withdrawn pursuant to the Offer satisfies the Minimum Tender Condition. All conditions to the Offer having been satisfied or waived, Purchaser has accepted for payment and will promptly pay for all such Shares in accordance with the Offer.

As a result of its acceptance of the Shares tendered in the Offer, Purchaser acquired a sufficient number of Shares to complete the Merger without a vote of the stockholders of the company pursuant to Section 251(h) of the DGCL. Accordingly, on February 16, 2017, Parent and Purchaser effected the Merger pursuant to Section 251(h) of the DGCL. Pursuant to the Merger Agreement, in the Merger, each Share that was issued and outstanding immediately prior to the Effective Time (other than Shares (i) owned by Parent, Purchaser or any other direct or indirect wholly-owned subsidiary of Parent immediately prior to the Effective Time, (ii) owned by the Company or any direct or indirect wholly-owned subsidiary of the Company or held in the Company’s treasury or (iii) held by a holder who is entitled to appraisal and who has properly exercised appraisal rights for such Shares in accordance with Section 262 of the DGCL) was converted automatically into the right to receive $24.00 in cash, net of applicable withholding taxes and without interest (which is the same amount per Share paid in the Offer). Following the Merger, all Shares will be delisted from NASDAQ and deregistered under the Exchange Act.

On February 16, 2017, Takeda issued a press release announcing the expiration and successful completion of the Offer and the consummation of the Merger. A copy of the press release issued by Takeda is attached hereto as Exhibit (a)(5)(A) and is incorporated herein by reference.”

Item 12. Exhibits

Item 12 of the Schedule TO is amended and supplemented by adding the following:

SIGNATURES

After due inquiry and to the best of their knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: February 16, 2017

EXHIBIT INDEX