United States

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the Month of September, 2018

Commission File Number: 001-35892

GW PHARMACEUTICALS PLC

(Translation of registrant’s name into English)

Sovereign House

Vision Park

Histon

Cambridge CB24 9BZ

United Kingdom

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F x Form 40-F ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):

¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):

¨

Other Events

On September 27, 2018, GW Pharmaceuticals plc along with its U.S. subsidiary, Greenwich Biosciences, announced that EPIDIOLEX® (cannabidiol) oral solution has been transferred to Schedule V, the lowest restriction classification, by the U.S. Drug Enforcement Administration. The press release is attached as Exhibit 99.1 hereto and is hereby incorporated by reference herein. The information contained in Exhibit 99.1 shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or incorporated by reference in any filing under the Securities Act of 1933, as amended unless expressly set forth by specific reference in such a filing.

Exhibits

99.1 Press release dated September 27, 2018

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, thereunto duly authorized.