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 13, 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):

Starting on January 13, 2014, representatives of Orexigen Therapeutics, Inc. (the “Company” or “Orexigen”) will be presenting to and conducting meetings with investors, analysts and others. During these presentations and meetings, the Company will present the slides attached as Exhibit 99.1 to this Current Report on Form 8-K, which is incorporated herein by reference.

The information in this Item 7.01 of this Current Report on Form 8-K, including Exhibit 99.1, is being furnished pursuant to Item 7.01 and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, and it shall not be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or under the Exchange Act, whether made before or after the date hereof, except as expressly set forth by specific reference in such filing to this item of this report.

* * *

By filing this Current Report on Form 8-K and furnishing this information, the Company makes no admission as to the materiality of any information in this report. The information contained in this report is intended to be considered in the context of the Company’s filings with the Securities and Exchange Commission (“SEC”) and other public announcements that the Company makes, by press release or otherwise, from time to time. The Company undertakes no duty or obligation to publicly update or revise the information contained in this report, although it may do so from time to time as its management believes is appropriate. Any such updating may be made through the filing of other reports or documents with the SEC, through press releases or through other public disclosure.

Orexigen cautions you that statements included in this report that are not a description of historical facts are forward-looking statements. Words such as “believes,” “anticipates,” “plans,” “expects,” “indicates,” “will,” “should,” “intends,” “potential,” “suggests,” “assuming,” “designed” and similar expressions are intended to identify forward-looking statements. These statements are based on the Company’s current beliefs and expectations. These forward-looking statements include statements regarding: the timing of potential approval of the NDA for NB 32; the benefit risk profile for NB 32; Orexigen’s plans to seek a commercialization partner in territories outside of North America; and the timing of the submission of the CSR for the interim analysis. 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 materially from those expressed or implied in this release due to the risk and uncertainties inherent in the Orexigen business, including, without limitation: the 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 NB 32 even after meeting the prespecified threshold and resubmitting the NDA; the possibility that the public announcement of the results of the 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; the potential for early termination of Orexigen’s North American collaboration agreement with Takeda Pharmaceutical Company Limited; the results from the interim analysis may not be sufficient to satisfy or respond to the Day 120 List of Questions from the EMA or any other data requirements of the EMA in connection with the review of the MAA; even if the NDA is approved by the FDA, the final results of the Light Study may not support continued approval of NB 32; the therapeutic and commercial value of NB 32; Orexigen’s ability to maintain sufficient capital to fund its operations through potential approval of NB 32 in 2014; 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 is included under the heading “Risk Factors” in Orexigen’s Current Report on Form 8-K filed with the Securities and Exchange Commission

on 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 Private Securities Litigation Reform Act of 1995.

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.

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