In children with the Dravet syndrome - a severe form of epilepsy - those given cannabidiol saw the median frequency of convulsive seizures drop from 12.4 to 5.9 per month - and 5 per cent of the children became entirely seizure free, a study in the New England Journal of Medicine has found.
"This is a major scientific breakthrough", says Professor Ingrid Scheffer, who is our Director of Paediatrics, one of the world's top epileptologists, and a contributing author of the study. "It's the first scientific evidence that cannabidiol works. There have been anecdotal reports in the past, and people with firm beliefs that it works in epilepsy, but this is the first time it's been proven."
Known as CBD, cannabidiol is a natural compound found in cannabis seeds, stalks and flowers. Studies have shown it does not have the psychoactive properties of THC.
Conducted for the Cannabidiol in Dravet Syndrome Study Group, the randomised, double-blind, placebo-controlled trial involved 120 children and young adults across the US and Europe. They received cannabidiol oral solution or a placebo, in addition to standard antiepileptic treatment.
Seizure frequency was measured over a 14-week treatment period. The median frequency of convulsive seizures per month decreased from 12.4 to 5.9 with cannabidiol, compared with a decrease from 14.9 to 14.1 with placebo.
There was no significant reduction in nonconvulsive seizures. Five per cent of patients taking cannabidiol became seizure-free, compared with none of the placebo group.
Side effects were more frequent in the cannabidiol group and included diarrhoea, vomiting, fatigue, increased body temperature, drowsiness and abnormal liver-function tests.
Professor Scheffer welcomed the findings. "I am delighted that we finally have high level evidence that cannabidiol is effective for uncontrolled seizures in Dravet syndrome," she says.
"Until now, there has only been anecdotal evidence but now we have scientific evidence proving that cannabidiol is definitely effective in epilepsy.
"The next question is whether cannabidiol is effective in other forms of epilepsy and it is great that there are trials already underway of cannabidiol in other groups of patients with epilepsy."