UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K/A

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 20, 2012

MannKind Corporation

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (661) 775-5300

N/A

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

This Current Report on Form 8-K/A is being filed by MannKind Corporation, a Delaware corporation (the “Company”), solely to correct certain information under Item 8.01 of the Company’s Current Report on Form 8-K filed with the Securities and Exchange Commission on December 24, 2012 (the “Original Report”). The Original Report incorrectly stated in the second paragraph under Item 8.01 that following the cancellation of the Cancelled Principal Amount (defined below) and the capitalization of the accrued and unpaid interest thereon, the total principal amount outstanding under the Note (defined below) was approximately $121.7 million, and that we had approximately $123.4 million available for borrowing under the Note. In actuality, as of immediately following the cancellation of the Cancelled Principal Amount and the capitalization of the accrued and unpaid interest thereon, the total principal amount outstanding under the Note was approximately $119.6 million (rather than $121.7 million) and we had approximately $125.4 million (rather than $123.4 million) available for borrowing under the Note.

In accordance with Rule 12b-15 of the Securities Exchange Act of 1934, as amended, the complete text of Item 8.01 (as amended) follows.

On December 21, 2012, following the approval by our stockholders of the amendment to our Amended and Restated Certificate of Incorporation and the filing of the Certificate of Amendment with the Secretary of State of the State of Delaware, we completed the closing (the “Closing”) of our previously announced issuance and sale of 40,000,000 unregistered shares of our common stock and unregistered warrants to purchase an aggregate of 30,000,000 shares of our common stock to The Mann Group LLC (“The Mann Group”), an entity controlled by our chief executive officer and principal stockholder, Alfred E. Mann, pursuant to the Common Stock and Warrant Purchase Agreement that we entered into with The Mann Group on October 18, 2012. The aggregate purchase price for the shares and warrants that we issued to The Mann Group was approximately $107.4 million and was paid for by cancelling principal indebtedness (the “Cancelled Principal Amount”) owed to The Mann Group under the Amended and Restated Promissory Note issued by us to The Mann Group on October 18, 2012 (the “Note”). The Cancelled Principal Amount became available for reborrowing under the Note upon the Closing. In accordance with the terms of the Note, we elected to capitalize the accrued and unpaid interest on the Cancelled Principal Amount that became due at the Closing.

Following the cancellation of the Cancelled Principal Amount and the capitalization of the accrued and unpaid interest thereon, the total principal amount outstanding under the Note was approximately $119.6 million, and we had approximately $125.4 million available for borrowing under the Note.

SIGNATURE

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

Dated: February 20, 2013