And scientists have found that the therapeutic effects can be gained without any need to "get high".

GW Pharmaceuticals is growing thousands of cannabis plants under a special Home Office licence with the ultimate aim of developing prescription medicines based on extracts of the drug.

Anecdotal evidence suggests that compounds extracted from the drug could benefit sufferers of multiple sclerosis, spinal cord injury, arthritis and chronic fatigue syndrome as well as a number of other problems.

The initial trials involved testing the impact of cannabis on six healthy volunteers. Much larger trials on ill patients are planned.

Dr Geoffrey Guy, the company chairman, said: "All the subjects came through very well, and we were very pleased with the study.

"Now we have a much better idea of what our starting point should be."

The results of the trial, conducted at an anonymous clinical pharmacology unit, will not be made public until they are disclosed in a scientific journal.

Many could be helped

But GW Pharmaceuticals has revealed that volunteers were given cannabis extracts either from an inhaler or via liquid under the tongue.

The main aim was to assess how well the treatments were tolerated and obtain an initial idea of the optimum dosage.

Heart rate, temperature and respiration were monitored and blood samples taken for analysis.

In addition each volunteer went through a battery of psychological tests.

Dr 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 said patients did not need to "get high" to gain a therapeutic benefit.

If approved by the regulatory authorities, the second phase trials will begin next year.

They will involve up to 300 patients with MS, spinal cord injury, and phantom limb pain.

By the end of the final phase three trials a total of around 2,000 patients will have taken part. The main studies should be completed in 2002.

GW Pharmaceutical's cannabis plants are housed in a highly secure and environmentally controlled glasshouse at a secret location in the home counties.