Exhibit 5.1

		12636 High Bluff Drive, Suite 400
		San Diego, California 92130-2071
		Tel: +1.858.523.5400 Fax: +1.858.523.5450
		www.lw.com
		FIRM / AFFILIATE OFFICES
		Abu Dhabi		Moscow
		Barcelona		Munich
		Beijing		New Jersey
		Boston		New York
		Brussels		Orange County
November 16, 2011		Chicago		Paris
		Doha		Riyadh
		Dubai		Rome
		Frankfurt		San Diego
		Hamburg		San Francisco
		Hong Kong		Shanghai
		Houston		Silicon Valley
		London		Singapore
		Los Angeles		Tokyo
		Madrid		Washington, D.C.
		Milan
Cadence Pharmaceuticals, Inc. 12481 High Bluff Drive, Suite 200 San Diego, CA 92130		File No. 036854-0031

Ladies and Gentlemen:

We have acted as special counsel to Cadence Pharmaceuticals, Inc., a Delaware corporation (the “Company”), in connection with the proposed issuance of up to 21,800,000 shares (the “Shares”) of common stock, $0.0001 par value per share (the “Common Stock”). The Shares are included in a registration statement on Form S-3 under the Securities Act of 1933, as amended (the “Act”), filed with the Securities and Exchange Commission (the “Commission”) on April 4, 2011 (File No. 333-173295) (as so filed and as amended, the “Registration Statement”), a base prospectus dated May 5, 2011 filed with the Commission in the Registration Statement (the “Base Prospectus”), a preliminary prospectus supplement dated November 14, 2011 filed with the Commission pursuant to Rule 424(b) under the Act (together with the Base Prospectus, the “Preliminary Prospectus”) and a prospectus supplement November 14, 2011 filed with the Commission pursuant to Rule 424(b) under Act (together with the Base Prospectus, the “Prospectus”). The Shares are being sold pursuant to an underwriting agreement dated November 14, 2011 between the Company and the underwriters named on Schedule A thereto (the “Underwriting Agreement”). This opinion is being furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement, the Preliminary Prospectus or Prospectus, other than as expressly stated herein with respect to the issue of the Shares.

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters. We are opining herein as to the

November 16, 2011

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General Corporation Law of the State of Delaware (the “DGCL”), and we express no opinion with respect to any other laws.

Subject to the foregoing and the other matters set forth herein, it is our opinion that, as of the date hereof, when the Shares shall have been duly registered on the books of the transfer agent and registrar therefor in the name or on behalf of the purchasers, and have been issued by the Company against payment therefor (not less than par value) in the circumstances contemplated by the Underwriting Agreement, the issue and sale of the Shares will have been duly authorized by all necessary corporate action of the Company, and the Shares will be validly issued, fully paid and nonassessable.

In rendering the foregoing opinion, we have assumed that (i) the Company will comply with all applicable notice requirements regarding uncertificated shares provided in the DGCL and (ii) upon the issue of any of the Shares, the total number of shares of Common Stock issued and outstanding will not exceed the total number of shares of Common Stock that the Company is then authorized to issue under its Amended and Restated Certificate of Incorporation.

We bring your attention to the fact that an investment fund affiliated with Latham & Watkins LLP and certain of the attorneys in this firm rendering legal services in connection with the offering own certain securities of the Company.

This opinion is for your benefit in connection with the Registration Statement and may be relied upon by you and by persons entitled to rely upon it pursuant to the applicable provisions of the Act. We consent to your filing this opinion as an exhibit to the Company’s Form 8-K dated November 16, 2011 and to the reference to our firm in the Prospectus under the heading “Legal Matters.” In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.