By Ben Hirschler
LONDON (Reuters) - An experimental cannabis drug failed to alleviate pain in cancer patients as hoped in a clinical study, sending shares in its British maker GW Pharmaceuticals as much as 21 percent lower on Thursday.
GW, which is developing the drug Sativex for pain in collaboration with Japan's Otsuka, said the first of three late-stage trials found no statistically significant difference between subjects using its product and those given a placebo.
GW Chief Executive Justin Gover said the findings were both disappointing and surprising, given encouraging results in earlier tests, but the company's scientists had not given up hope.
Results from two further Phase III trials are due later this year and, if positive, could still allow the drug to be submitted for treating pain in patients with advanced cancer, where it is designed to be given on top of opioids.
"Although we missed the primary endpoint in this trial, based upon the positive data seen in the Phase II programme, we remain confident in the ability for Sativex to relieve cancer pain in this patient population,” Gover said.
Shares in GW, which have been on a roll on hopes for its so-called cannabinoid medicines since the firm listed on Nasdaq in 2013, fell as much as 21 percent before paring losses to stand 5 percent lower by 1350 GMT.
Sativex, which is given as an under-the-tongue spray, is already approved for treating spasticity caused by multiple sclerosis in 27 countries, although not yet in the United States.
In addition to trying to expand Sativex's use into pain relief, GW is also developing other cannabis-derived drugs. One of these, Epidiolex, has produced promising results in children with hard-to-treat epilepsy and GW said work on this programme was on track or ahead of schedule.
Phase III data on Epidiolex in treatment-resistant epilepsy is now expected by the end of 2015.
Interest in the medical effects of cannabis has been spurred recently by the legalisation of recreational marijuana shops in Colorado and Canada's move to create a federally regulated medical marijuana industry.
But GW, which grows cannabis under licence at a secret location in Britain, distances itself from this by emphasising its ability to extract key ingredients for medical use, in the same way that painkillers have been developed from opium.
(Editing by Pravin Char; editing by Susan Thomas)