Among patients with multiple sclerosis (MS) use of cannabis extract helps ease painful muscle stiffness, states trial.
The "Phase III" test -- the final stage in a process to vet a new drug or medical process -- took place among 22 centres in Britain.
Over 12 weeks, 144 patients were given daily tablets of tetrahydrocannabinol, which is the active ingredient in cannabis, and 135 were given a dummy pill, also called a placebo.
At the end of the study, 29.4 percent of people in the cannabis group said they had experienced relief from muscle spasms, compared to 15.7 percent in the placebo group, according to an 11-point rating.
They also reported improvement in sleep quality. Side effects were nervous system disorders and gut problems, but none was severe.
MS, a disease that affects the brain and spinal cord, occurs when the immune system attacks the fatty myelin sheaths that insulate nerve cells.
Painful stiffness in the muscles occurs among up to 90 percent of patients at some time, often leading to poor sleep and impaired mobility.
The trial, led by John Peter Zajicek of Britain's Clinical Neurology Research Group, says standardised doses of cannabis extract can be useful in easing pain and spasms in this disease.
Previous Phase III trials on cannabis and MS have thrown up conflicting results, partly because of the scale by which users report any change in their symptoms, the MUSEC researchers said.