Shares in the UK’s GW Pharmaceuticals sank on Friday after an inquest ruled that its cannabis-derived drug Sativex (tetrahydrocannabinol plus cannabidiol) was linked to the death of Rene Anderson, a 69-year-old diabetic, who took part in trials of the drug in 2003.

The coroner in the case concluded that: “On the balance of probabilities, an idiosyncratic reaction [defined as unusual, unexpected and individual] to a trial drug (either alone or in combination with other medications) was at least a significant contributory factor to the initiation of this illness.”

Mrs Anderson took part in a three-week study of Sativex during October 2003, and died the following March. However, in a statement, GW said that it did not believe “it raises any new or additional safety concerns about Sativex.”

It also stressed that Mrs Anderson took a very low dose of the drug over a short period of time, and that her care had been complicated by her taking a wide range of other medicines during a four-month stay in hospital. The company was also quick to point out that confusion is listed on the product information as an effect linked to Sativex, but says that in the rare cases where it has been seen, it has fully reversed on withdrawal.

Dr Stephen Wright, R&D Director of GW, said: “It does not mean that Sativex is dangerous for patients even if it may have been one of several factors to have caused Mrs Anderson’s initial confusion. All relevant information concerning this case was passed to the regulatory authorities at the time according to standard procedures and has been included in all safety information subsequently provided to clinicians and regulators. We do not believe that this case has any negative consequences for the regulatory progress of Sativex.”

Sativex, which is sprayed into the mouth, is GW's leading product and first won first approval for use as a treatment for neuropathic pain in Canada in April after a somewhat rocky road to market. However, things have been looking up, and GW signed a £46 million deal with Spain’s Almirall Prodesfarma for the drug last week.