THE beneficial effects of a cannabis cigarette on a disturbed patient has prompted psychiatrists to investigate the potential mental health advantages of the drug.

Senior psychiatrist Professor Heather Ashton, of Newcastle University, said cannabis could have an important role to play in easing the symptoms of severe mental illness.

A team at Newcastle University is reviewing scientific literature about the use of cannabis in relation to the treatment of "bipolar" mental illnesses, such as manic depression and schizophrenia.

On the basis of that review, the Newcastle psychiatric team has recommended that scientific trials of cannabis as a possible treatment for mental illness should be undertaken.

Because cannabis-based drugs are still illegal in the UK it is likely that such a trial would take place in Canada.

Prof Asthon said it was a single case which convinced her department to look at the evidence on cannabis.

"We had a case of a chap who gets manic episodes. He gets very violent and unruly and has been sectioned five times. One of the psychiatrists involved in our paper was called out to see him because they were about to section him again," the professor said.

"By the time he got there this chap was sitting serenely on the sofa smoking cannabis. It was clear that was what calmed him down. An hour before he had been unrestrainable," she said.

Cannabis has also been used by multiple sclerosis sufferers who say it helps them to control spasms.