(by John Bingham, Peter Dominiczak, Camilla Turner, London’s Daily Telegraph) – One in four new cases of psychotic conditions such as schizophrenia could be the direct result of smoking extra-strong varieties of cannabis (marijuana), a major new British study concludes.

The finding suggests that about 60,000 people in Britain are currently living with conditions involving hallucinations and paranoid episodes brought on by abuse of high-potency cannabis, known as skunk, and more than 300,000 people who have smoked skunk will experience such problems in their lifetime.

The six-year study, the first of its kind in Britain, calculates that daily users of skunk are five times more likely to suffer psychosis than those who never touch it.

Psychiatrists said there is now an “urgent need” for a drive to educate the public about the risks involved with the substance. It is believed that even newer varieties, some of them more than twice as potent as those currently available on British streets, have already been developed in the Netherlands.

The findings reopen the debate about the classification of cannabis as an illegal drug in Great Britain, with some supporters of liberalization now considering tougher restrictions on some varieties.

Chris Grayling, the Justice Secretary, said the findings underlined arguments against decriminalization.

Norman Baker, the Liberal Democrat former Home Office minister who has called for drug laws to be relaxed, said that there may be a case for giving skunk a new classification.

The study, by researchers from the Institute of Psychiatry, Psychology & Neuroscience at King’s College London, is due to be published in the journal Lancet Psychiatry later this week.

Researchers studied almost 800 working-age adults from one area of south London, half of whom had been recently treated for a psychotic episode for the first time.

The incidence of schizophrenia in the area has doubled since the mid-Sixties, a trend widely thought to be linked to drug use.

Cannabis use in the UK overall has fallen by about 40 percent in the past decade but, for those using it, the typical potency has increased sharply in that time.

Levels of tetrahydrocannabinol (or THC), the main psychoactive compound, are about 15 percent in skunk, compared with about 4% in traditional “hash” cannabis.

The study concluded that the strength of cannabis and the frequency of use play a crucial role in determining the mental health risks.

“Compared with those who never used cannabis, individuals who mostly used skunk-like cannabis were nearly twice as likely to be diagnosed with a psychotic disorder if they used it less than once per week, almost three times as likely if they used it at weekends, and more than five times as likely if they were daily users,” the paper notes.

It found that skunk use was the “strongest predictor” of psychotic illness in those studied and that 24 percent of new cases in the area could be attributed to skunk.

It also noted that those who started smoking cannabis before the age of 15 had higher risk of developing psychotic disorders than others.

“Our findings show the importance of raising public awareness of the risk associated with use of high-potency cannabis, especially when such varieties of cannabis are becoming more available,” the paper concludes.

“The worldwide trend of liberalization of the legal constraints on the use of cannabis further emphasizes the urgent need to develop public education to inform young people about the risks of high-potency cannabis.”

Dr. Marta Di Forti, the lead author, said the significance of how regularly people smoked cannabis has often been overlooked in day-to-day treatment.

“When a GP or psychiatrist asks if a patient uses cannabis it’s not helpful – it’s like asking whether someone drinks,” she said. “As with alcohol, the relevant questions are how often and what type of cannabis.”

Prof Sir Robin Murray, professor of psychiatric research at King’s, said: “It is now well known that use of cannabis increases the risk of psychosis. However, skeptics still claim that this is not an important cause of schizophrenia-like psychosis.

“This paper suggests that we could prevent almost one quarter of cases of psychosis if no-one smoked high potency cannabis.”

He added: “Education is the important thing – people need to know the risks of regular use of high potency cannabis.

Mr. Grayling said: “Far too many of those who end up in our criminal justice system have got drug and mental health problems.

“It’s clear to me that drug addiction is at the root of a large proportion of crimes in the UK and that it causes mental health problems which are all too apparent in our prisons.

“That’s why mental health will be our next big reform focus – but it’s also why decriminalization is not the right option.”

Mark Winstanley, the chief executive of Rethink Mental Illness, said: “Essentially, smoking cannabis is like playing a very real game of Russian roulette with your mental health. Reclassifying cannabis isn’t the answer.”

A British Home Office spokesman said: “Our approach remains clear: we must prevent drug use in our communities and help dependent individuals through treatment and recovery, while ensuring law enforcement protects society by stopping supply and tackling the organized crime that is associated with the drugs trade.” …

Marjorie Wallace, chief executive of the mental health charity SANE, said:

“This is yet another study that should worry all those who deny any direct link between skunk, a potent cannabis derivative, and psychotic breakdown.

“While the scientists and politicians debate, we face the daily heartbreak of young people whose minds and thoughts have been altered through continued use and whose families feel helpless.

“What we need is a strong, uncompromising message so that parents, teachers, the police and young people themselves know that a significant percentage who take skunk risk acute, and in some cases lasting, mental illness.”

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