A British pharmaceutical firm is conducting research into the therapeutic uses of the drug, with the aim of producing prescription medicines derived from cannabis.

Cannabis is widely believed to benefit people suffering from multiple sclerosis, arthritis, spinal cord injury and chronic fatigue syndrome. It also reportedly helps treat the eye condition, glaucoma.

While doctors in Britain have on occasion admitted to prescribing cannabis to patients suffering from extremely painful conditions, evidence of long term medical benefit is purely anecdotal.

But now, the UK-based GW Pharmaceuticals, is studying the medical effects of cannabis as part of its development of a prescription drug. The cultivation and possession of cannabis is illegal, and the company is operating under a speciallicence from the British Home Office. Its early trials on healthy human volunteers have shown that, administered therapeutically, the drug is unlikely to cause the user any harm.

GW Pharmaceuticals' early findings and research methods will be audited by regulatory authorities. If approved, the company will begin the second stage of trials next year. If everything goes to plan the main body of research, and three stage trials involving 2000 patients, will be completed by 2002 .

The company's initial trials on human volunteers were aimed at assessing how well the treatments were tolerated, and to work out what combination of active ingredients have the greatest impact and what the optimum dosage of the drug might be.

The volunteers were administered a standardised cannabis extract either as a liquid, under their tongue for direct absorption into the blood stream or from an inhaler, not dissimilar to ones used by asthma sufferers. Each volunteers' heart rate, temperature and respiration were monitored andblood analysed.

They were also subject to rigorous psychological tests. GW Pharmaceutical's chairman, Dr Geoffrey Guy said: ``We have been able to define and follow through the psychoactive effects. None of the effects is disturbing, or would be classed in a clinical trial as serious.''

He pointed out that most people using cannabis for medical reasons did not want to get ``high.'' He said: ``They want the pain to be eased without unwanted side effects so that they can get on with their lives.''

For those who have endlessly debated which strain of the cannabis is best, scientists at GW Pharmaceuticals say that for their purposes cannabis sativa, is best. Normally grown for its flowers rather than its resin, sativa was found to contain the most effective pain-relieving strain.