UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 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): January 7, 2014

OREXIGEN THERAPEUTICS, INC.

(Exact Name of Registrant as Specified in its Charter)

Registrant’s telephone number, including area code: (858) 875-8600

(Former Name or Former Address, if Changed Since Last Report.)

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 (see General Instruction A.2. below):

On January 7, 2014, Orexigen Therapeutics, Inc. (the “Company” or “Orexigen”) announced that the United States Food and Drug Administration (“FDA”) has assigned a Prescription Drug User Fee Act (“PDUFA”) goal date of June 10, 2014 for the review of the resubmitted New Drug Application (“NDA”) for Contrave^®.

Orexigen cautions you that statements included in this report that are not a description of historical facts are forward-looking statements. These forward-looking statements include statements regarding the exact timing of the completion of the FDA’s review of the Contrave NDA and the potential for, and timing of, approval of the Contrave NDA. The inclusion of forward-looking statements should not be regarded as a representation by Orexigen that any of its plans will be achieved. Actual results may differ from those set forth in this report due to the risk and uncertainties inherent in the Orexigen business, including, without limitation: the potential for the FDA to delay the scheduled PDUFA goal date of June 10, 2014 due to the FDA’s internal resource constraints or other reasons; the Special Protocol Assessment (“SPA”) is not binding on the FDA if public health concerns unrecognized at the time the SPA agreement was entered into become evident, other new scientific concerns regarding product safety or efficacy arise, or if Orexigen fails to comply with the agreed upon trial protocol; the potential for the FDA to not approve Contrave even after meeting the prespecified threshold and resubmitting the NDA; the possibility that the public announcement of the results of the Light Study interim analysis would later be deemed to jeopardize the integrity of the Light Study potentially resulting in the requirement to conduct additional, costly studies; additional analysis of the interim results or new data from the continuing Light Study, including safety-related data, may produce negative or inconclusive results, or may be inconsistent with the conclusion that the interim analysis was successful; the potential that the interim analysis may not be predictive of future results in the Light Study; and other risks described in Orexigen’s filings with the Securities and Exchange Commission. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof, and Orexigen undertakes no obligation to revise or update this report to reflect events or circumstances after the date hereof. Further information regarding these and other risks included under the heading “Risk Factors” in Orexigen’s Current Report on Form 8-K filed with the Securities and Exchange Commission December 2, 2013 and its other reports, which are available from the SEC’s website (www.sec.gov) and on Orexigen’s website (www.orexigen.com) under the heading “Investor Relations.” All forward-looking statements are qualified in their entirety by this cautionary statement. This caution is made under the safe harbor provisions of Section 21E of the Securities Exchange Act of 1934.

SIGNATURES

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.