Research could soon show that cannabis could be a helpful long-term treatment for multiple sclerosis sufferers.

Patients who took part in a 15-week study - published in the Lancet last year - went on to try the effectiveness of the banned drug for a 52-week course, John Zajicek of the Peninsula medical school told the British Association science festival which ended in Exeter yesterday.

"Initial results of the longer-term study are positive and will be published in the near future. In the short-term study, there was some evidence of cannabinoids alleviating symptoms of multiple sclerosis; in the longer term there is a suggestion of a more useful beneficial effect, which was not clear at the initial stage," he said in a statement.

"I hope these results will encourage support of further studies of cannabinoids in multiple sclerosis and, potentially, other diseases."

Cannabis has been used as a medical treatment for at least as long as it has been a recreational drug. Queen Victoria is supposed to have used it for period pains. It was sometimes used in childbirth and a poignant archaeological discovery in the Middle East revealed cannabis remnants near the body of a young woman who probably died in childbirth 5,000 years ago.

Cancer patients have claimed that cannabis could help suppress nausea after chemotherapy. Glaucoma sufferers have claimed it relieves pressure on the eyeball and delays the onset of blindness.

Animal experiments have suggested the drug slows nerve cell death. And many multiple sclerosis sufferers have been using it, illegally, to relieve the pain and stiffness of their slow progression towards helplessness.

Once it became clear that cannabis-like chemicals were produced naturally in the human nervous system to control appetite and facilitate nerve cell communication, researchers began to understand why a folk remedy could be medically effective.

But clinical evidence in randomised double-blind trials has been rare. "We set out to establish whether there was any scientific truth behind that," Dr Zajicek said.

A total of 667 patients took part in a short-term study. More than 500 agreed to go on to longer trials. The patients were given either capsules containing cannabis extract, an active component of the drug called THC, or sugar pills. The chief aim had been relief of muscle stiffness.

"But we also wanted to look at the other symptoms, including pain, bladder disturbance and measures of disability," he said. "From the patient's symptomatic point of view there was beneficial effect but we couldn't prove that from an independent assessment by a physiotherapist of muscle stiffness."

So they continued the trials: the results could be published in a few weeks' time.

Researchers are notoriously unwilling to discuss results before they have been reviewed by their peers and published formally in a scientific journal. "What I can say at the moment is that there does seem to be evidence of some beneficial effect in the longer term that we didn't anticipate in the short term study."