GW Pharmaceuticals Release: Sativex(R) Enters Phase III Clinical Program in Cancer

Porton Down, UK; 23 November 2010: GW Pharmaceuticals plc (AIM: GWP) today announces the initiation of the Phase III clinical trials programme of Sativex® in the treatment of pain in patients with advanced cancer, who experience inadequate analgesia during optimized chronic opioid therapy. This indication represents the initial target indication for Sativex in the United States.

The Phase III 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.

The primary efficacy measure of the Phase III trials is a patient assessment of pain using a 0-10 Numeric Rating Scale (NRS), and the primary analysis is the “continuous response analysis of percent improvement from baseline” (an analysis of percent improvement in pain across the spectrum of response levels). This analysis has yielded statistically significant results in both the Phase IIa and IIb trials and has been the key efficacy parameter discussed in the product labeling of several recently approved medicines in the US for pain. The dose range employed in the studies is 3 – 10 sprays per day.

The Phase III programme follows the announcement earlier this year of positive data from a Phase IIb trial. Since this time, GW and Otsuka have met with the Food & Drug Administration (FDA) at an “end of Phase II” clinical meeting to review the Phase II clinical data and the Phase III trial design. GW and Otsuka are also currently engaged in discussions with the FDA regarding other aspects of the development plan.

Each of the Phase III trials is expected to recruit patients in Europe, North America, Latin America and Asia. The first Phase III trial site has now been initiated in Europe and the first patient is expected to be recruited during December 2010. The principal investigator of the first study is Dr. Russell K. Portenoy, Chairman of the Department of Pain Medicine and Palliative Care at Beth Israel Medical Center in New York City. The second Phase III study is expected to commence in mid 2011.

The Phase IIb trial evaluated three dose ranges of Sativex® – a low dose (1-4 sprays per day), mid dose (6-10 sprays per day), and high dose (11-16 sprays per day) over a 5 week treatment period. In this study, the continuous response analysis showed statistically significant results in favor of Sativex for both the Sativex® low and mid dose groups versus placebo (p=0.008 and p=0.038, respectively). The low and mid dose Sativex® groups, when combined, were also significantly superior to placebo for the primary outcome measure (p=0.006) and for the important secondary efficacy measure of reduction in sleep disruption (p=0.016).

The results of this Phase IIb dose ranging study were consistent with a previous Phase IIa, 3-week clinical trial in 177 patients. In this prior study, Sativex® showed a statistically significant improvement versus placebo in the continuous response analysis of improvement in average daily pain (p=0.044). This study was been published in the Journal of Pain and Symptom Management1.

Dr. Stephen Wright, GW’s R&D Director, said, “We are pleased to have arrived at this important milestone in the development of Sativex® for cancer pain. Sativex® aims to address the needs of the many patients with advanced cancer who do not attain adequate pain relief from an opioid regimen. We have completed two large Phase II trials with positive results and look forward to working with Otsuka on this comprehensive Phase III programme for Sativex® in this important indication.”

Sativex® is approved in the UK, Spain, Canada and New Zealand as a treatment for Multiple Sclerosis (MS) spasticity and GW aims to seek approval for Sativex® in this MS indication across Europe and other selected markets. Cancer pain represents the initial target indication for Sativex® in the US. It is intended that the Phase III cancer pain data will also be used by GW for future regulatory applications in this indication in Europe and around the world.

1 Johnson J et al, Journal of Pain and Symptom Management, Vol 39, Issue 2, pp 167-179 Enquiries: For GW: GW Pharmaceuticals plc Today: +44 20 7831 3113 Dr Geoffrey Guy, Chairman Thereafter: + 44 1980 557000 Justin Gover, Managing Director Mark Rogerson, Press and PR Tel: + 44 7885 638810 Financial Dynamics Tel: +44 20 7831 3113 Ben Atwell, John Dineen

Sativex® Sativex® is an investigational new product composed primarily of two cannabinoids: CBD (cannabidiol,) and THC (delta 9 tetrahydrocannabinol). Sativex® is administered as a metered dose oro-mucosal spray each 100µL spray contains 2.7mg THC and 2.5mg CBD. The Sativex® formulation is standardized by both composition and dose and is supplied in small spray vials. The components of Sativex® have been shown to bind to cannabinoid receptors that are distributed throughout the central nervous system and in immune cells.

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

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

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