She can't do it herself because she is badly affected by multiple sclerosis. But, as the first puff of cannabis seeps into her bloodstream, the pain in her legs and arms begins to ease. She is able to plan a trip to the shops without suffering the constant pain that even large amounts of morphine and codeine previously failed to touch. Nor does cannabis produce the side-effects she experiences with nabilone, a synthetic relation of cannabis legally prescribed at her doctor's discretion.
Susan is by no means alone. All over the country, sufferers from various disorders vouch for the relief that cannabis brings them. Yet no clear scientific evidence of its efficacy exists. In the UK, it has been illegal for a doctor to prescribe cannabis since 1971. To do research requires a licence from the Home Office, authorisation that is so hard to get that few scientists have bothered. As a result, most of the evidence about the beneficial effects of cannabis is purely anecdotal.
Last month, however, the Royal Pharma-ceutical Society published a detailed review of the subject in The Pharmaceutical Journal. It found that the strongest evidence in favour of cannabis came from patients, like Susan Marriner, with muscle spasm and tremor brought on by MS or cerebral palsy. Cannabis also lowers pressure in the eyeball, and has been used successfully to treat patients with glaucoma - the eye disease that leads to tunnel vision and blindness.
A small number of studies have also found that cannabis can be useful in treating epileptics who are not helped by other forms of treatment. Chronic pain also seems to respond well to the drug, and its relaxant effect on the airways of the lungs has made it a successful treatment for asthma. The down side, however, is that smoking cannabis irritates the already over-reactive airways of asthma patients. To be useful to them, it would have to be administered in some other way.
In fact, it is the idea of authorising a substance that would be smoked - rather than the principle of issuing an illegal drug on prescription - that can cause most concern. This certainly seemed true of Government ministers, as a delegation from the Alliance for Cannabis Therapeutics (ACT) discovered when they went to the Department of Health in October last year, But smoking is not the only way that cannabis can be absorbed into the blood. Some people take it as a herbal tea, others bake it in scones or cakes. - but it is difficult to maintain a constant, reliable dose.
In the Netherlands, a marijuana research institute has been set up to get around this problem. Plants are cloned to produce cannabis of a standard quality and purity, and doctors are developing new formulations - such as an aerosol spray - so that patients don't need to smoke the drug. "We prescribe a medicinal grade of the herb," says Dr Robert Trossel of the Preventive Medical Centre in Rotterdam. "When patients go to the pharmacy, they get a constant, high-standard drug rather than the variable quality they may be able to buy at their coffee shop."
Problems getting sufficiently pure cannabis led a spinal injury patient, John Brown (not his real name), to grow his own plants. An amateur botanist, he has carefully crossed plants grown from American and Dutch seed to produce a hybrid. This provides the ideal mix of cannabis to relieve the arthritic pain in his neck which he gets as a result of a motorcycle accident over 20 years ago.
"Before I started with cannabis I was taking a high dose of codeine 11 times a day, and it took me a while to get off it. Now I smoke a small joint at night so I can sleep and each joint lasts me three nights. I'm completely off all my other painkillers," he explains.
In his loft are six precious cannabis plants; what he doesn't need he gives to MS sufferers and other patients. If he was discovered, he could be charged with dealing as well as possessing cannabis.
At 64, Antonia White is a criminal too. She uses cannabis to relieve the muscle spasms she gets in her arms as a result of cerebral palsy. She discovered its muscle-relaxing properties 20 years ago when she tried some that her daughter had brought home. "I was a very relaxed sort of mum," she says, "and I thought I'd have a go. I was amazed when the spasm just dropped out of my arm. It was really dramatic."
When her daughter left home, Antonia went back to conventional mecicines, but nothing ever worked as well. So now she smokes a cannabis cigarette about four times a week, usually in the evening when her arms are more prone to spasm.
Dr William Notcutt, a consultant anaesthetist and member of the Alliance for Cannabis Therapeutics, is investigating how to get around the problem of smoking cannabis by developing alternative ways of administering it. "We want to put it on the same therapeutic footing as heroin and morphine, which we can prescribe for pain relief," he says, "so it must be in a form that is medically suitable for clinicians. We need a slow route, prob-ably oral, for patients who need a long-acting, background level of drug - and we also need a quick-acting form for patients who need an immediately effect - MS patients, for example."
It's a Catch 22 situation, Dr Notcutt points out. The Department of Health won't license a product unless it is pharmaceutically pure, but companies aren't interested in developing a cannabis product. They are put off by the bureaucracy concerning an illegal drug, and the fact that it will have a limited market and not be very profitable.
One thing in cannabis's favour is it safety record. There have been no known deaths from cannabis overdose and in the small amounts used to treat symptoms of MS and other conditions, few patients experience the euphoric effects sought by social users. Physical dependence is rare because the drug is very soluble in fat and lingers in the body for long periods, so that people do not get noticeable withdrawal effects as they do with heroin.
Following its analysis of current knowledge the Royal Pharmaceutical Society has come down in favour of scientific trials to establish, once and for all, what sort of role cannabis should have in medicine. Recognising that such research could take some time to get off the ground, it has recommended that doctors be allowed to prescribe cannabinoids for named serious disorders, at least for a trial period.
At Aberdeen University, Dr Roger Pertwee, a pharamacologist, has spent 25 years doing laboratory research on cannabis. In the last five years, scientists have begun to understand how the drug works on the body. For example, they now knows that it acts on specific sites in the brain called CB1 receptors, and perhaps more curiously at sites on immune cells called CB2 receptors, where it seems to have an immunosuppresant effect.
But as Dr Pertwee points out, these receptors haven't evolved just in case people decided to start smoking cannabis. In 1992 the body's natural form of cannabis, called anandamide, was discovered. Since then, cannabis receptor blockers have been developed that can reverse the effects of cannabis and anandamide. Since high doses of cannabis can impair memory, cannabis antagonist drugs could, in theory, be used to treat memory disorders.
Dr Pertwee is currently completing a survey of UK patients who use cannabis to treat their symptoms. Having established how people are using the drug, he hopes to get funding for scientific trials of cannabis in MS. For Clare Hodges, co-founder of ACT in the UK, such studies would be just reward for years of lobbying on behalf of patients who turned to cannabis out of desperation, when they had exhausted everything conventional medicine had to offer.
"There has been so much resistance to the idea that cannabis can have therapeutics uses," she says. "I assume this is because the campaign has been largely patient-led. Our experiences are valued far less than doctors' observations. We're supposed to be passive - and patient!"
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