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): July 21, 2015

Chiasma, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code (866) 637-9703

Not Applicable

(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:

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

As previously disclosed in the Registration Statement on Form S-1 (File No. 333-204949) (the “Registration Statement”) of Chiasma, Inc. (the “Company”), on July 21, 2015 and in connection with the consummation of the initial public offering (the “IPO”) of shares of common stock of the Company, Dror Brandwein and Vincent Miles, Ph.D. resigned from the Company’s board of directors. The resignations of Mr. Brandwein and Dr. Miles were not caused by any disagreement with the Company.

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

As previously disclosed in the Registration Statement, on July 21, 2015 and in connection with the consummation of the IPO, the Company filed an amended and restated certificate of incorporation (the “Restated Certificate”) with the Secretary of State of the State of Delaware. The Company’s board of directors and stockholders previously approved the Restated Certificate to be filed in connection with, and to be effective upon, the consummation of the IPO. The Restated Certificate amends and restates the Company’s certificate of incorporation in its entirety to, among other things: (i) authorize 125,000,000 shares of common stock; (ii) eliminate all references to the previously-existing series of preferred stock; and (iii) authorize 5,000,000 shares of undesignated preferred stock that may be issued from time to time by the Company’s board of directors in one or more series.

The foregoing description of the Restated Certificate is qualified by reference to the Restated Certificate, a copy of which is attached hereto as Exhibit 3.1 and is incorporated herein by reference.

In addition, as previously disclosed in the Registration Statement, on July 21, 2015 and in connection with the consummation of the IPO, the amended and restated by-laws of the Company (the “Amended and Restated By-Laws”), previously approved by the Company’s board of directors and stockholders to become effective immediately upon the consummation of the IPO, became effective. The Amended and Restated By-Laws amend and restate the Company’s by-laws in their entirety to, among other things: (i) eliminate the ability of the Company’s stockholders to take action by written consent in lieu of a meeting and call special meetings of stockholders; (ii) establish procedures relating to the presentation of stockholder proposals at stockholder meetings; (iii) establish procedures relating to the nomination of directors; and (iv) conform to the amended provisions of the Restated Certificate.

The foregoing description of the Amended and Restated By-Laws is qualified by reference to the Amended and Restated By-Laws, a copy of which is attached hereto as Exhibit 3.2 and is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

(d) 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