The medical research council is to spend £500,000 on a controversial trial to see whether or not cannabis can relieve the pain of patients who have undergone surgery, it was announced yesterday.
The trial will enroll 400 patients, in spite of a strongly worded and critical review by eminent pain scientists published in the British Medical Journal in July 2001.
The review looked at trials of synthetic cannabinoids derived from cannabis. It found that the substances worked no better than codeine in relieving post-operative pain. The cannabinoids also depressed the central nervous system, limiting their use.
"Their widespread introduction into clinical practice for pain management is therefore undesirable. In acute post-operative pain they should not be used," the authors said.
Henry McQuay, professor of pain relief at the Nuffield department of anaesthetics at Oxford's Churchill hospital, said yesterday that the review team, of which he had been a member, stood by the findings and that he was surprised at the MRC announcement.
"To get the analgesic equivalent to low-dose codeine you were taking a dose [of cannabinoids] which gave you a lot of side effects. It didn't seem to us that it was a good bet, to put it politely," he said.
Professor McQuay, who is clinical editor of the journal Pain, said that at his clinic he found patients with neuropathic pain [from nerve damage] who had smoked cannabis without relief.
"It's like alcohol. If you are lucky it makes you feel better, which is slightly different from shifting the pain," he said.
But the leader of the MRC trial, Anita Holdcroft, of Imperial College and the Chelsea and Westminster hospital, said that no comparison could be made between the post-operative pain trials she would be conducting and those that Prof McQuay and his colleagues had reviewed. "The studies [reviewed in the BMJ] were looking at a synthetic cannabinoid, which is quite different from using the cannabis plant material," she said. "You can't make broad statements that all the drugs don't work when it only relates to one particular type of drug.
"We don't have the evidence for cannabis; until we do the trial we won't ... There are no studies of cannabis in post-operative pain so to say it cannot be used when nobody has ever done it is inappropriate."
Dr Holdcroft's involvement stems from the early 1990s when she wrote a paper on cannabis use with a patient suffering acute to chronic pain.
The MRC trials will use a capsule holding a standardised extract of the entire cannabis plant. Patients awaiting surgery in at least 36 British hospitals will be invited to join the trial. Those tested will, randomly, get either extracts of the cannabis plant, one of its active ingredients, a standard pain-relieving drug, or a placebo. Neither they nor their doctors will know what they have been given.
Turning cannabis into a medicine has become a political as well as scientific issue, especially since the Lords' science and technology committee urged trials to take place in 1998. Many multiple sclerosis sufferers say smoking cannabis relieves their symptoms.
GW Pharmaceuticals has conducted the required three phases of trials on an oral spray derived from cannabis. A spokeswoman for the multinational firm Bayer, which has signed an agreement to help market the drug, said it was not known whether it would be months or even a year or more before the spray was approved or rejected.
GW Pharmaceuticals is also doing trials with cancer patients, but has not pursued the area of post-operative pain.
Easing suffering: Potential uses
Multiple sclerosis Many patients have for years claimed their symptoms are relieved by cannabis, which they smoke or eat. Some have been taken to court for possession, which has caused an outcry. The House of Lords science and technology committee took their part when it called for trials of cannabis use in MS in 1998, and returned to the issue in 2001, demanding urgent action to get cannabis products regulated for medicinal use. The MS Society estimated that 1% of 35,000 people with the disease were using the drug illegally.
Neuropathic pain There is evidence, particularly from animal studies, that cannabis relieves pain from damaged nerves. Pains such as those from amputation do not respond well to narcotics.
Anti-nausea Clinical trial evidence exists showing cannabis can suppress the nausea and vomiting experienced by cancer patients as a result of chemotherapy. Studies in the 1970s showed that nabilone, a synthetic derivative, was as effective as other anti-nausea drugs and it was licensed as a medicine, but it is little used.
Anorexia Cannabis has been used to tempt people with eating disorders and lack of appetite. But in regular users the effect is thought to wear off.
