An experimental cannabis-based drug from GW Pharmaceuticals has successfully treated children with a rare form of epilepsy, sending the company’s shares soaring and more than doubling its stock market value.

GW said a clinical trial showed its Epidiolex drug had significantly reduced seizures in patients with Dravet syndrome, a type of epilepsy for which there are currently no treatments approved in the US, compared to a placebo. In the trial of 120 patients, those taking Epidiolex saw a reduction of monthly convulsive seizures of 39% compared with 13% for a placebo, which GW said was highly statistically significant. The company’s chief executive Justin Gover said:

The positive outcome of this Phase 3 trial is a significant milestone in the development of Epidiolex as a potential new treatment for patients suffering from Dravet syndrome. We are excited about the potential for Epidiolex to become the first [US Food and Drug Administration] approved treatment option specifically for Dravet syndrome patients and their families.

The study is the first of four epilepsy trials, and GW now plans to ask for a meeting with the FDA to discuss its plans to seek regulatory approval for the treatment.

GW was founded in 1998 to explore the medical benefits of cannabis, and its multiply sclerosis treatment Sativex now has approval in more than 20 countries, although not in the US. The company has a UK government licence to grow cannabis plants for medical use.

News of the successful Epidiolex trial has pushed its shares up 123% to 481.75p.