UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-Q/A

Amendment No. 1

For the quarterly period ended June 30, 2016

Or

For the transition period from                      to                     .

Commission file number: 000-50865

MannKind Corporation

(Exact name of registrant as specified in its charter)

(661) 775-5300

(Registrant’s telephone number, including area code)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  x    No  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act).    Yes  ¨    No  x

As of August 1, 2016, there were 478,048,448 shares of the registrant’s common stock, $0.01 par value per share, outstanding.

EXPLANATORY NOTE

This Amendment No. 1 on Form 10-Q/A (this “Amendment”) amends the Quarterly Report on Form 10-Q of MannKind Corporation for the quarter ended June 30, 2016, originally filed with the Securities and Exchange Commission on August 9, 2016 (the “Original Filing”). We are filing this Amendment for the sole purpose of correcting certain errors in the Interactive Data Files included with the Original Filing as Exhibit 101 thereto. Amended Interactive Data Files are filed with this Amendment as Exhibit 101.

In connection with the filing of this Amendment and pursuant to the rules of the Securities and Exchange Commission, we are also filing with this Amendment a new certification pursuant to Rule 13a-14(a) or 15d-14(a) of the Securities Exchange Act of 1934, as amended, by our Chief Executive Officer and Chief Financial Officer, which is attached to this Amendment as Exhibit 31.

Except as described above, no other changes have been made to the Original Filing. The Original Filing continues to speak as of the date of the Original Filing, and we have not updated the disclosures contained therein to reflect any events which occurred at a date subsequent to the filing of the Original Filing other than as indicated in this Amendment.

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 thereunto duly authorized.

EXHIBIT INDEX