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): December 2, 2014

Regulus Therapeutics Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (858) 202-6300

N/A

(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):

Item 5.03 Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year.

On December 2, 2014, the Board of Directors of Regulus Therapeutics Inc. (the “Company”) approved the amendment and restatement of the Company’s bylaws (as amended and restated, the “Bylaws”), effective immediately, in order to add a forum selection provision for the adjudication of certain disputes. The new provision, set forth in Section 49 of the Bylaws, provides that, unless the Company consents in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware (or, if the Court of Chancery does not have jurisdiction, another state court located within the State of Delaware or, if no state court located within the State of Delaware has jurisdiction, the federal district court for the District of Delaware) shall, to the fullest extent permitted by law, be the sole and exclusive forum for (i) any derivative action or proceeding brought on behalf of the Company; (ii) any action asserting a claim of breach of a fiduciary duty owed by any director, officer or other employee of the Company to the Company or the Company’s stockholders; (iii) any action asserting a claim against the Company or any director or officer or other employee of the Company arising pursuant to any provision of the General Corporation Law of the State of Delaware, the Company’s Certificate of Incorporation (as may be amended from time to time) or the Bylaws (as may be amended from time to time); and (iv) any action asserting a claim against the Company or any director or officer or other employee of the Company governed by the internal affairs doctrine.

A copy of the Bylaws is attached to this report as Exhibit 3.1.

Item 9.01 Financial Statements and Exhibits.

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.

EXHIBIT INDEX