UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. )

Filed by the Registrant x

Filed by a Party other than the Registrant o

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o	Preliminary Proxy Statement
o	Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))
o	Definitive Proxy Statement
x	Definitive Additional Materials
o	Soliciting Material under §240.14a-12

Cubist Pharmaceuticals, Inc.
(Name of Registrant as Specified In Its Charter)


(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

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CUBIST PHARMACEUTICALS, INC. Important Notice Regarding the Internet Availability of Proxy Materials for the Annual Meeting of Stockholders to be held on June 3, 2014 at the Company’s offices at 55 Hayden Avenue, Lexington, MA 02421 This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. The Proxy Statement and Annual Report to Stockholders are available at http://viewproxy.com/cubist/2014/ If you want to receive a paper or e-mail copy of these documents, you must request one. There is no charge to you for requesting a copy. Please make your request for a copy as instructed below on or before May 23, 2014 to facilitate timely delivery. Important information regarding the Internet availability of the Company’s proxy materials, instructions for accessing your proxy materials and voting online and instructions for requesting paper or e-mail copies of your proxy materials are provided on the reverse side of this Notice. STOCKHOLDERS ARE CORDIALLY INVITED TO ATTEND THE ANNUAL MEETING AND VOTE IN PERSON. To the Stockholders of CUBIST PHARMACEUTICALS, INC. Notice is hereby given that the Annual Meeting of Stockholders of Cubist Pharmaceuticals, Inc. will be held on Tuesday, June 3, 2014 at 8:30 a.m. Eastern Daylight Time at the Company’s offices at 55 Hayden Avenue, Lexington, MA 02421 for the following purposes: 1. Election of Class III nominees of the Board of Directors: 01 – Michael Bonney, 02 – Jane Henney, M.D., 03 – Leon Moulder, Jr. 2. Advisory vote to approve the compensation paid to our Named Executive Officers. 3. Approval of the amendment to our Restated Certificate of Incorporation to increase the number of authorized shares of common stock from 150,000,000 to 300,000,000. 4. Approval of our 2014 Employee Stock Purchase Plan. 5. Approval of our 2014 Omnibus Incentive Plan. 6. Ratification of our selection of PricewaterhouseCoopers LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2014. Proposals — The Board of Directors recommends a vote “FOR” all the nominees listed in Proposal 1 and “FOR” Proposals 2, 3, 4, 5 and 6. INTERNET TELEPHONE E-MAIL CONTROL NO. The Securities and Exchange Commission rules permit us to make our proxy materials available to our stockholders via the Internet. Material for this annual meeting and future meetings may be requested by one of the following methods: To view your proxy materials online, go to http://viewproxy.com/cubist/2014/. Have the 11 digit control number available when you access the website and follow the instructions. 877-777-2857 TOLL FREE requests@viewproxy.com * If requesting material by e-mail, please send a blank e-mail with the company name and your 11 digit control number (located below) in the subject line. No other requests, instructions or other inquiries should be included with your e-mail requesting material. You must use the 11 digit control number located in the box below.

CUBIST PHARMACEUTICALS, INC. 55 Hayden Avenue Lexington, MA 02421 The following proxy materials are available to you to review at: www.viewproxy.com/cubist/2014/ • 2013 Annual Report • Proxy Statement Directions to attend the meeting can be found on the Company’s website, www.cubist.com ACCESSING YOUR PROXY MATERIALS ONLINE Have this notice available when you request a paper copy of the proxy materials or to vote your proxy electronically. You must reference your control number to vote by internet or request a hard copy. You May Vote Your Proxy When You View The Material On The Internet. You Will Be Asked To Follow The Prompts To Vote Your Shares. Your electronic vote authorizes the named proxies to vote your shares in the same manner as if you marked, signed, dated and returned the proxy card. Internet and telephone voting is available through 2:00 A.M. Eastern Daylight Time on June 3, 2014. REQUESTING A PAPER COPY OF THE PROXY MATERIALS By telephone please call 1-877-777-2857 toll free or By logging onto http://viewproxy.com/cubist/2014/ or By email at: requests@viewproxy.com Please include the company name and your control number in the subject line.