Science Correspondent James Wilkinson: Scientists believe trials will be successful

Dr Anita Holdcroft from Hammersmith Hospital in London will test whether cannabis or its active components can be used to relieve post-operative pain.

Three hundred patients will take part.

Dr John Zajicek of Derriford Hospital in Plymouth will begin a trial on 600 patients into whether cannabis is effective in treating muscular rigidity in multiple sclerosis sufferers.

The doctors volunteered to take part in trials after a meeting of experts in London on Monday.

The experts from the Royal Pharmaceutical Society (RPS) and the Medical Research Council published protocols on how to carry out clinical trials on cannabis.

Legalising cannabis

If the results of the trials are accepted by the World Health Organisation, they could lead to the UK government legalising cannabis for medical use.

It is expected to take six months to set them up them.

The RPS said that if the trials proved the drug was beneficial named patients could be prescribed the drug within three years.

The protocols which are behind the two trials are the result of a Working Party on the Therapeutic Use of Cannabinoids set up by the RPS in 1998.

They relate specifically to cannabis use for people with multiple sclerosis and post-operative pain.

Health Correspondent Richard Hannaford: Still some time before drugs made from cannabis are prescribed

Professor Tony Moffat, chief scientist at the RPS, said: "We are delighted that Dr Anita Holdcroft and Dr John Zajicek have volunteered to lead these important trials into the the therapeutic use of cannabis.

"Trials conducted in line with the new protocols established by the working party should offer conclusive, scientific evidence that a standardised preparation of cannabis and tetrahydrocannabinol have therapeutic benefit."

The Multiple Sclerosis Society, which was represented on the RPS working party, has welcomed the protocols.

Clare Hodges wants cannabis on prescription now

Clare Hodges, from the Alliance for Cannabis Therapeutics has used cannabis to treat her own multiple sclerosis for several years. She called for the drug to be available on prescription while research was undertaken.

She said: "We are delighted cannabis is eventually being taken seriously in trials.

"But thousands of people have got multiple sclerosis now. I cannot put my multiple sclerosis on hold for seven years until it is available.

"Thousands of us use cannabis now in potentially quite a dangerous way. We have to buy it off the street and we don't know the quality of what we are getting."

But Dr Griffith Edwards, editor of the journal Addiction, said the scientific benefit of cannabis had to be proven before the drug should be made widely available in any form.

He said: "You need a controlled trial which determines in what dose over what period the drug is effective for what conditions, with what downside as well as what upside, and whether it works better than other drugs.

"To be ruled by a hunch, even by compassion, is not the way to go. You may put a drug onto the market a drug which does not work very well and even does harm."

A recent House of Lords Science and Technology Committee report backed the medicinal use of cannabis.

Patients with certain illnesses, such as multiple sclerosis, say it relieves their symptoms.

The Lords' report forwarded the case for the legalisation of cannabis

The Lords report said recreational use of cannabis should remain illegal, but proposed listing cannabis as a "schedule two" drug - downgrading it from its current prohibited "schedule one" status.

The committee estimated that about 1% of MS patients already used cannabis for pain relief, effectively making themselves criminals.

However, the government ruled out the committee's recommendation that cannabis be made available on prescription.

It called for more clinical trials before a change in the drug laws could be considered.

Smoking

Doctors were also critical of the report, saying they backed the medicinal use of cannabinoids, part of the cannabis plant.

They believe the plant itself causes harmful side-effects.

The fact that smoking is currently the preferred way of taking it also increases health risks, they say.

The drugs firm GW Pharmaceuticals is growing thousands of cannabis plants at a secret glasshouse facility in the south of England for medical research.

It is the first to get special Home Office licences allowing it to grow and supply the drug for research purposes. An initial crop of 5,000 plants was sown in August at a secure glasshouse in the south of England.

Eventually 20,000 plants will be grown there.

GW has developed a special inhaler device for taking measured amounts of cannabis.