Previously, support for medicinal marijuana has been based on anecdotal data. Now there could be science backing it.
A new study published on Thursday (NZ time) has found medicine made from a marijuana extract can dramatically cut the number of seizures experienced by children with a severe form of epilepsy.
It's the first time a double-blind placebo-controlled trial has been done on it.
The research has excited the doctors who led the study, which was published in the New England Journal of Medicine, as it finally provides reliable data as opposite to anecdotal.
"More than 26 percent of the children who received the drug had a significant reduction in their convulsive, or severe seizures compared to the placebo group so it was a very positive finding, it was statistically significant and more importantly, it was clinically significant," lead researcher Dr Orrin Devinsky said.
"Some of those children were actually seizure-free and many others enjoyed a substantial reduction in their seizure frequency."
In the trial, neither the parents nor the researchers were told whether the children were taking the study medication or the placebo.
It was tested with 120 children who had Dravet syndrome, chosen at random from the US, the UK and parts of Europe.
Sixty one got the study medication, while 59 were on the placebo.
Patients on the drug dropped from around 12 serious seizures a month, to six. Those on the placebo didn't change, according to Dr Devinsky.
The medication was a liquid form of cannabidiol, one of marijuana's ingredients, branded Epidiolex. It doesn't contain any THC.
There are currently no drugs specifically approved for Dravet, which is a rare form of genetic epilepsy.
Up to 20 percent of those with the condition die by the time they're 20.
"Today for the first time we have rigorous, double blind, placebo controlled trial that cannabidiol works in reducing convulsive seizures in children with severe epilepsy," Dr Devinsky said.
But he cautioned it wasn't a cure-all - side effects such as diarrhoea, vomiting, fatigue, sleep problems and other issues were more common in the group taking the drug.