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

April 17, 2015

Date of Report (Date of earliest event reported)

Auspex Pharmaceuticals, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (858) 558-2400

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

Item 7.01 Regulation FD Disclosure.

On April 17, 2015, Auspex Pharmaceuticals Inc. (the “Company”) published a poster entitled “A Phase 3 Trial of Deutetrabenazine for the Treatment of Chorea Associated with Huntington Disease” on the website of the American Academy of Neurology (“AAN”) (www.aan.com), which is furnished herewith as Exhibit 99.1. The Company is scheduled to present the poster at the 2015 AAN Annual Meeting that will take place on April 18-25, 2015, in Washington D.C.

Forward-Looking Statements.

Statements contained in, or incorporated by reference into, 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. 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 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.

The information contained in this Item 7.01 and Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities and Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits

SIGNATURE

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

EXHIBIT INDEX