Shares in GW Pharmaceuticals were on the up this morning on London's Stock Exchange after the firm announced it had secured the backing of Canada's drug regulatory agency for its cannabis-derived drug Sativex in treating cancer pain.

Specifically, Health Canada has given the green light to Sativex (delta-9-tetrahydrocannabinol and cannabidiol) for treating moderate to severe breakthrough pain in advanced cancer patients already being given the highest tolerated doses of opioid medicines, such as morphine. The approval has been granted under Canada's fast-track system for medicines that have already demonstrated "promising benefit" and "possess an acceptable safety profile", but means GW must collate more data to back this up through additional trials.

Two years ago, Health Canada took the plunge by giving Sativex the nod for treating nerve pain in patients with multiple sclerosis, while other countries (notably the UK) has spent a considerable amount of time deliberating over the fact it is derived from the cannabis plant. Last month in Europe, GW pulled its application for the drug in treating MS spasticity after it was asked for additional data to support the dossier, triggering an almost 30% nosedive in its share price. It plans to re-file in 2008.

Sativex is delievered via a spray pump into the mouth and is thought to act via cannabinoid receptors that are distributed throughout throughout the pain pathways of the nervous system. In trials, more than 40% of patients given Sativex on top of their background pain medication experienced a further clinically important reduction in pain.

“Cancer pain is not managed as well as it could be and the resources available to manage cancer pain effectively are still somewhat limited. Cannabinoids have an important role in treating complex cancer pain particularly neuropathic pain and demonstrate a positive effect with current treatment options,” said Dr Lawrence Librach, Director of the Temmy Latner Centre for Palliative Care at Mount Sinai Hospital and Vice President of the Canadian Hospice Palliative Care Association.

According to the Canadian Cancer Society, 39% of Canadian women and 44% of men will develop cancer during their lifetimes. And, of those who go on to develop advanced cancer, 60% to 90% will experience moderate to severe pain.

Sativex is marketed in Canada by Bayer.