Interview: psychiatrist Robin Murray

Psychiatrist Robin Murray had never really planned on studying the effects of cannabis on mental health. Rather, he found himself falling into it after noticing that some of his patients, who had been gradually climbing out of the well of schizophrenia, were having relapses after smoking the occasional spliff.

"Day in, day out, I was going to either my outpatient clinic or my inpatient unit and we'd have a patient who would do brilliantly," he says. If they did particularly well, the patients would be allowed to go out for the evening, to enjoy themselves. "The next morning [they] would be psychotic, hearing voices and quite deluded again." And whenever this happened, there was usually one main suspect: the patient had probably smoked cannabis the night before.

Anecdotes like this will only serve to increase the furore currently going on in middle England about cannabis: next week the drug will be reclassified from class B to C, putting it on the same level as steroids and tranquillisers. Possession could still result in up to two years in prison but it is widely thought that the police will not bother to prosecute the majority of cases. Experts have attempted to allay fears of a flood of cannabis on the streets, suggesting that usage is unlikely to jump when the drug is reclassified. But recently the focus of concern has been the long-term psychological effects of the active ingredient in cannabis - tetrahydrocannabinol - and newspapers have been filled with personal horror stories about the harmful effects of the drug.

It was these concerns that led Murray, a professor of psychiatry at the Maudsley hospital in south London and one of Britain's leading experts on mental health, to carry out investigations into the relationship between cannabis and mental health. What he found was that cannabis almost always exacerbated symptoms of psychosis in people who were already suffering from (or had a family history of) any mental health problems.

"We studied people who recently developed [schizophrenia], then followed them up after four years," says Murray of the initial studies. "The people who were taking cannabis when we first met them and continued taking cannabis were doing three times worse than people who had never taken cannabis. In particular, they still had some of the positive symptoms of schizophrenia."

At that point, Murray began to look deeper. "It's a bit like saying, 'Well, if people with chronic bronchitis smoke, this is not good for their chronic bronchitis'," he says."Then you begin to think, could smoking contribute to developing chronic bronchitis in the first place? Then we started thinking about the question of whether cannabis could contribute to the onset of [psychosis]."

Murray's latest work echoed the results of previous research by one of his colleagues, lecturer Louise Arsenault. "What Louise did was to collaborate with researchers in New Zealand who had been following a series of about 1,000 children from birth. These children had been interviewed throughout their childhood and they'd been followed up right to age 26, when they were all given a psychiatric interview."

Arsenault realised that the research subjects had been interviewed about their drug consumption when they were 15 and then again when they were 18. And this allowed her to work out whether cannabis had any effect on their later risk of schizophrenia-like psychoses.

In November 2002, Arsenault's team published her results in the highly respected British Medical Journal.

"The conclusion was that, if you took cannabis at age 18, you were about 60% more likely to go psychotic. But if you started by the time you were 15, then the risk was much greater, around 450%," says Murray.

The research also showed that if children with quasi-psychotic ideas (in other words, they thought that other children were ganging up against them or they heard voices at a young age) took cannabis, they were also especially vulnerable to mental illness in later life.

All of this provided good evidence that there was a link between cannabis and the onset of psychosis. But it did not explain what cannabis was actually doing in the brains of the patients. Indeed, the physiological effects of cannabis are not fully understood.

"The brain produces substances rather like cannabis which are part of normal brain function," says Murray. "One of the reasons why we get an effect from cannabis is because there actually are cannabinoid receptors in the brain. We suspect that the reason why cannabis is related to psychosis is that the cannabinoid receptors are closely related to other receptors called dopamine receptors." All drugs that increase the brain's dopamine levels (cocaine and amphetamine for example), are known to increase the chances of having a psychotic episode. Indeed, all the drugs that psychiatrists use to stop the episodes block these very receptors.

So will the reclassification of the drug next week mean a sudden increase in cases for the likes of Murray?

Murray says he is agnostic about the issue."To be frank, in south London, it doesn't matter what the classification is. People who want cannabis can get it; it is readily available," he says.

"What I think is much more important is that the public should know that cannabis is actually a drug."

This is not as simple as it might seem. Murray relates a common story in his clinics about patients who claim never to take drugs.

"Many of our patients, when we say to them, 'Are you taking any drugs?', say, 'No, I would never touch drugs.' Then you say, 'What about cannabis?' Oh, yes, comes the reply. Of course they take cannabis - in fact, they take cannabis every day but surely that's just a herb, it's a natural substance? That couldn't do any harm, they say.

"There is a general view that cannabis is not really a drug and if it is a drug, it is a safe drug," says Murray. "I'm not saying that the reclassification shouldn't go ahead. What I'm saying is that ministers and others when they talk about cannabis should say that a few puffs here and there, a couple of spliffs is not going to do you much harm but taking daily cannabis for a number of years will indeed increase your risk of schizophrenia."

Murray compares the dangers of cannabis to those of everyone's favourite drug, alcohol.

"Somehow people know that a glass of wine or an occasional beer is different from taking a bottle of whisky every day for five years," he says.

And in some ways, the current situation with cannabis can even be likened to the attitudes to cigarettes more than 50 years ago.

"The situation is a bit like in the 1950s, when people were beginning to say, 'If you smoke for 20 years, this can increase your risk of lung cancer.' It took a long time to do the big epidemiological studies and then to do the exact studies to examine the mechanisms," says Murray.

One reason why our understanding of long-term cannabis use is poor is that there has been no government-funded research in the area, according to Murray. And the problem is getting critical.

"This is the biggest problem that psychiatrists in the inner cities see - that in so many of our patients, cannabis has been a contributing factor and so many of them do badly because of the cannabis they keep taking," says Murray.

But Murray does not want to be alarmist. "Any fool knows that half the world smokes cannabis and they don't all go psychotic. What we're trying to find out is why do some people go psychotic and others don't," he says. "Obviously, cannabis does not readily induce psychosis in people who have no vulnerability.There's a range of vulnerability in the general population and it is those people who have a heavy predisposition, say somebody has a family history of schizophrenia, cannabis can light up their illness and in which case it can be very difficult to totally reverse. But somebody who has just a brief psychotic reaction and has no other pre-disposing factors, then I think there's a very good chance that they will be OK."

And, despite his background, Murray does not see a role for himself in preaching to people about whether cannabis is a good or a bad thing. "Certainly, around our part of the world, they're not going to pay attention to a 59-year old professor of psychiatry," he says. "I don't think it's a particularly useful thing for somebody like me to come over heavy-handed and say that under no circumstances should you smoke cannabis when all their peer pressure will be to smoke cannabis. If people want to smoke cannabis, they have the right to do so."

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