UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 8-K

Current Report

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 22, 2015

RETROPHIN, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (646) 837-5863

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

On May 22, 2015, Retrophin, Inc. (the “Company”) entered into an Asset Purchase Agreement (the “Purchase Agreement”) with Sanofi pursuant to which the Company has agreed to sell Sanofi its Rare Pediatric Disease Priority Review Voucher (the “Asset Sale”), which was awarded by the U.S. Food and Drug Administration to encourage development of new drugs and biologics for the prevention and treatment of rare pediatric diseases.

Pursuant to the Purchase Agreement, Sanofi will pay the Company $150.0 million upon the closing of the Asset Sale, plus an additional $47.5 million on the first anniversary of the closing of the Asset Sale and an additional $47.5 million on the second anniversary of the closing of the Asset Sale.

The closing of the Asset Sale is subject to customary closing conditions, including the expiration or termination of the required waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended. The parties have made certain representations, warranties, and covenants in the Purchase Agreement.

The foregoing description of the terms of the Purchase Agreement is qualified in its entirety by reference to the Purchase Agreement, a copy of which is attached hereto as Exhibit 2.1 and incorporated herein by reference.

Forward-Looking Statements

Statements contained in this Current Report on Form 8-K regarding matters that are not historical facts are “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. Because such statements are subject to risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. Among the factors that could cause actual results to differ materially from those indicated in the forward-looking statements are risks and uncertainties associated with the Company’s ability to close the Asset Sale. Risks are described more fully in the Company’s filings with the Securities and Exchange Commission, including without limitation the Company’s most recent Annual Report on Form 10-K, as amended, Quarterly Report on Form 10-Q and other documents subsequently filed with or furnished to the Securities and Exchange Commission. All forward-looking statements contained in this Current Report on Form 8-K speak only as of the date on which they were made. The Company undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date on which they were made.

(d) Exhibits

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.