The first clinical trials in the world are to be carried out here to see if cannabis really does ease the pain of multiple sclerosis.
The Medical Research Council has approved a grant of almost a million pounds to fund the research at a hospital in Plymouth.
In recent years several patients with MS have been prosecuted for using the drug, as ITN's Andrea Catherwood reports.
Marijuana is illegal in Britain, but sufferers of multiple sclerosis swear it eases their pain.
Research has been done into the claims before - but never - anywhere in the world has a proper clinical trial been run.
MS specialists have fought for years for these tests which could be an crucial step to legalising the drug.
Dr Lorna Layward of the Multiple Sclerosis Society said: "This is a major step.
"This is the first very large clinical trial. If this trial should show that cannabis is of medicinal use, is of benefit in the treatment of spasticity, it would be a major step in getting the drug reshechulded so that doctors could use it for medicinal purposes."
For 17 years Claire Hodges has battled MS an incurable disease attacking her nervous system.
Her tea is laced with cannabis as it is the most effective drug she has found.
"I spent nine years taking drugs and medicines from doctors, and some of it worked a bit and some of it made me much worse," she said.
"But cannabis is certainly the most useful medicine I have taken in 17 years of having this condition."
The results of the trial will not be known for three years.
So for now, Britain's 85,000 MS sufferers will still be breaking the law if they chose to take the drug to ease their symptoms.