Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2020	Apr. 23, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K/A
Amendment Flag	true
Amendment Description	EXPLANATORY NOTE GW Pharmaceuticals plc (the “Company” or “we” or “us” or “GW”) is filing this Amendment No. 1 on Form 10-K/A (this “Amendment”) to amend our Annual Report on Form 10-K for the year ended December 31, 2020 (the “Original Form 10-K”), originally filed with the Securities and Exchange Commission (the “SEC”) on February 26, 2021 (the “Original Form 10-K”), to include the information required by Items 10 through 14 of Part III of our Form 10-K. This information was previously omitted from our Form 10-K in reliance on General Instruction G(3) to Form 10-K, which permits the information in the above referenced items to be incorporated in our Form 10-K by reference from our definitive proxy statement if such statement is filed no later than 120 days after our fiscal year-end. We are filing this Amendment to include Part III information in our Form 10-K because a definitive proxy statement containing such information will not be filed by April 30, 2021. Except as otherwise expressly noted herein, this Amendment does not modify or update in any way the financial position, results of operations, cash flows, or other disclosures in, or exhibits to, the Original Form 10-K, nor does it reflect events occurring after the filing of the Original Form 10-K. Accordingly, this Amendment should be read in conjunction with the Original Form 10-K. In addition, as required by Rule 12b-15 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), new certifications by the Company’s principal executive officer and principal financial officer are filed herewith as exhibits to this Amendment pursuant to Rule 13a-14(a) or 15d-14(a) of the Exchange Act. As no financial statements have been included in this Amendment and it does not contain or amend any disclosure with respect to Items 307 or 308 of Regulation S-K, paragraphs 3, 4, and 5 of the certifications have been omitted. The Company is not including certifications pursuant to Section 1350 of Chapter 63 of Title 18 of the United States Code (18 U.S.C. 1350) as no financial statements are being filed with this Amendment.
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Registrant Name	GW PHARMACEUTICALS PLC
Entity Central Index Key	0001351288
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Document Annual Report	true
Document Transition Report	false
Entity File Number	001-35892
Entity Incorporation, State or Country Code	X0
Entity Tax Identification Number	00-0000000
City Area Code	+44
Local Phone Number	1223 266800
Entity Address, Address Line One	Sovereign House
Entity Address, Address Line Two	Vision Park
Entity Address, Address Line Three	Chivers Way, Histon
Entity Address, City or Town	Cambridge
Entity Address, Postal Zip Code	CB24 9BZ
Entity Address, Country	GB
Entity Common Stock, Shares Outstanding		378,535,952
Entity Public Float			$ 3,735,551,435
ICFR Auditor Attestation Flag	true
Title of 12(b) Security	American Depositary Shares, each representing 12 Ordinary Shares, par value £0.001 per share
Trading Symbol	GWPH
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE None.

GW PHARMACEUTICALS PLC 10-K/A