The House of Lords committee considering the case for legalising cannabis for medical use heard of its positive benefits last week.
Roger Pertwee, president of the International Cannabinoid Research Society and reader in biomedical sciences at the University of Aberdeen, told the Lords science and technology committee that he was "pretty convinced" by the anecdotal evidence from multiple sclerosis sufferers of the benefits of cannabis.
He called on the Department of Health to organise large-scale clinical trials. "Cannabis is already being used, albeit illegally," Dr Pertwee said. "It is important that trials start as soon as possible."
Dr Pertwee said that a small number of clinical trials have been undertaken to evaluate the effects of cannabinoids, a set of 60 chemicals found in cannabis, in reducing pain and spasticity. The size of the samples, however, has been quite small.
Pharmaceuticals companies, which normally sponsor such developments, have steered clear of cannabis and cannabinoids. "With cannabis widely available, drug companies probably wonder why they should develop an expensive drug when people can get hold of cannabis relatively easily," Dr Pertwee said.
He also stressed the need for more basic science to investigate whether the physiological and psychological effects of cannabis can be separated.
Dr Pertwee said there are still many questions that need to be answered before a clinical trial can be undertaken. Should a clinical trial include a single cannabinoid or cannabis, with its associated negative effects? Many MS sufferers say that cannabis is more effective than individual cannabinoids. How should it be administered? Smoking gives very instant relief and allows self-regulation, but could also lead to lung cancers, while oral administration gives variable results. And how can the end effects be judged? There would be difficulties undertaking a double-blind test on a drug that has associated psychological effects - a placebo may be easily apparent.
Dr Pertwee's call for trials follows earlier evidence given to the Lords from the British Medical Association, which called for more research into developing synthetic forms of cannabis to avoid unwanted side effects, including that of the associated "high".
Before the committee, Heather Ashton, a clinical psychiatric pharmacologist at Newcastle University, stressed the carcinogenic properties of smoked cannabis: one joint gives the same risk of chest trouble as five cigarettes. She also said that there is evidence that cannabis is addictive and can impair memory and coordination over long periods.
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