€11.9 Million Milestone Payment

April 16, 2012

Porton Down, UK; 16 April 2012: GW Pharmaceuticals plc (AIM: GWP) confirms that it has now earned the €11.9 million milestone payment due as a result of the recently amended terms of its licence agreement with Almirall S.A. (announced on 15 March 2012). This milestone reflects the revised terms of the expanded collaboration between GW and Almirall and is in recognition of the achievement of a specified patient recruitment target in the Sativex® Phase III cancer pain trial programme. GW expects to receive payment of the milestone next month.

Enquiries:

GW Pharmaceuticals plc

(Today) + 44 20 7831 3113
Dr Geoffrey Guy, Chairman

(Thereafter) + 44 1980 557000
Justin Gover, Managing Director

FTI Consulting

+ 44 20 7831 3113
Ben Atwell / John Dineen

Peel Hunt LLP

+44 207 418 8900
James Steel / Vijay Barathan

Notes to Editors

About GW
GW was founded in 1998 and listed on the AIM, a market of the London Stock Exchange, in June 2001. Operating under license from the UK Home Office, the company researches and develops cannabinoid pharmaceutical products for patients who suffer from a range of serious ailments, in particular multiple sclerosis and cancer pain. GW has assembled a large in-house scientific team with expertise in cannabinoid science as well as experience in the development of both plant-based prescription pharmaceutical products and medicines containing controlled substances. GW occupies a world leading position in cannabinoids and has developed an extensive international network of the most prominent scientists in the field. For further information, please visitwww.gwpharm.comThis news release may contain forward-looking statements that reflect GWs current expectations regarding future events, including development and regulatory clearance of the GW’s products. Forward-looking statements involve risks and uncertainties. Actual events could differ materially from those projected herein and depend on a number of factors, including (inter alia), the success of the GW’s research strategies, the applicability of the discoveries made therein, the successful and timely completion of uncertainties related to the regulatory process, and the acceptance of Sativex® and other products by consumer and medical professionals.