GW Pharmaceuticals: Receipt of Milestone Payment

Porton Down, UK; 17 January 2011: GW Pharmaceuticals plc (AIM: GWP) confirms that following its announcement on 23 November 2010 that the Phase III clinical trials programme of Sativex® in cancer pain had been initiated, the first patient was randomized in Europe as anticipated in December 2010. As a result, and in accordance with the terms of GW’s licence agreement with Otsuka Pharmaceutical Co. Ltd, GW has received a milestone payment from Otsuka of $4 million.

Enquiries:

GW Pharmaceuticals plc (Today) + 44 20 7831 3113

Dr Geoffrey Guy, Chairman (Thereafter) + 44 1980 557000 Justin Gover, Managing Director

Financial Dynamics + 44 20 7831 3113 Ben Atwell / John Dineen

Peel Hunt LLP +44 207 418 8900 James Steel / Vijay Barathan

Sativex in Cancer Pain

Cancer pain represents the initial target indication for Sativex® in the United States. Sativex® is approved in the UK, Spain, Canada and New Zealand as a treatment for Multiple Sclerosis spasticity.

The Phase III cancer pain programme is being performed in conjunction with GW’s licensing partner for Sativex® in the US, Otsuka Pharmaceutical Co. Ltd. The programme, which is fully funded by Otsuka, includes two Phase III randomised placebo-controlled multi-centre multinational trials as well as a long term extension study. Each Phase III trial will include approximately 370 patients and will evaluate the efficacy and safety of Sativex versus placebo over a 5 week treatment period.

Cancer Pain

Studies suggest that more than one-third of patients with cancer, and more than three-quarters of those with advanced disease, have chronic pain. Large surveys indicate that optimal opioid therapy does not yield sufficient relief in a substantial proportion of these patients.

About GW-Otsuka

In February 2007, GW and Otsuka entered into a major long term strategic alliance. The relationship commenced with the signing of an exclusive license agreement to develop and market Sativex®, GW’s lead product, in the US. In July 2007, GW and Otsuka signed a global research collaboration for the study of cannabinoids in the field of Central Nervous System (CNS) and oncology to research, develop and commercialize a range of candidate cannabinoid products.

About Otsuka Pharmaceutical Co., Ltd

Founded in 1964, Otsuka Pharmaceutical Co.,Ltd. is a global healthcare company with the corporate philosophy 'Otsuka-people creating new products for better health worldwide.' Otsuka researches, develops, manufactures and markets innovative and original products, with a focus on pharmaceutical products for the treatment of diseases, and consumer products for the maintenance of everyday health. Otsuka is committed to being a corporation that creates global value, adhering to high ethical standards required of a company involved in human health and life, maintaining a dynamic corporate culture, and working in harmony with local communities and the natural environment. Otsuka Pharmaceutical Co., Ltd. is a wholly owned subsidiary of Otsuka Holdings Co., Ltd., the holding company for the Otsuka Group. The Otsuka Group comprises 145 companies and employs approximately 39,000 people in 23 countries and regions worldwide. Otsuka and its consolidated subsidiaries earned ¥1,084.2 billion (approx. US $11.7 billion) in annual revenues in fiscal 2009. For more information, visit www.otsuka.co.jp/en

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 visit www.gwpharm.com

This 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.

Juliet Edwards Assistant Financial Dynamics Holborn Gate, 26 Southampton Buildings London, WC2A 1PB D +44 (0)20 7269 7125

www.fd.com

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