EX-5.1

Exhibit 5.1

LOGO

Sean M. Clayton

+1 858 550 6034

sclayton@cooley.com

August 7, 2018

MannKind Corporation

30930 Russell Ranch Road, Suite 301

Westlake Village, California 91362

Ladies and Gentlemen:

You have requested our opinion, as counsel to MannKind Corporation, a Delaware corporation (the “Company”), with respect to certain matters in connection with the filing by the Company of a Registration Statement on Form S-8 (the “Registration Statement”) with the Securities and Exchange Commission, covering the offering of up to 24,442,045 shares of the Company’s Common Stock, $0.01 par value (the “Shares”), including (i) 3,000,000 shares (the “ESPP Shares”) reserved for issuance pursuant to the Company’s 2004 Employee Stock Purchase Plan (the “ESPP”) and (ii) 21,442,045 shares (the “EIP Shares”) reserved for issuance pursuant to the Company’s 2018 Equity Incentive Plan (the “EIP,” and collectively with the ESPP, the “Plans”).

In connection with this opinion, we have examined and relied upon the Registration Statement and related prospectuses, the Plans, the Company’s Amended and Restated Certificate of Incorporation, as amended, its Amended and Restated Bylaws and the originals or copies certified to our satisfaction of such records, documents, certificates, memoranda and other instruments as in our judgment are necessary or appropriate to enable us to render the opinion expressed below. We have assumed the genuineness and authenticity of all documents submitted to us as originals and the conformity to originals of all documents submitted to us as copies thereof.

Our opinion is expressed only with respect to the General Corporation Law of the State of Delaware

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the ESPP Shares, when sold and issued in accordance with the ESPP, and the EIP Shares, when sold and issued in accordance with the EIP, and in each case when sold and issued in accordance with the Registration Statement and the related prospectuses, will be validly issued, fully paid, and nonassessable (except as to shares issued pursuant to certain deferred payment arrangements, which will be fully paid and nonassessable when such deferred payments are made in full).

COOLEY LLP 4401 EASTGATE MALL SAN DIEGO, CA 92121

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