CANNABIS LINK TO PSYCHOSIS DEPENDS ON AGE

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CANNABIS LINK TO PSYCHOSIS DEPENDS ON AGE OF FIRST USE


Half of regular smokers of cannabis who are psychologically vulnerable to its effects may end up needing treatment for psychosis, scientists said yesterday.


Up to 10 per cent of the adult population, almost four million people, has a tendency to paranoid thoughts or grandiose ideas and may be tipped into psychotic delusions by the effects of the drug, they said.


A four-year study of 2,437 people aged 14 to 24 found that of those who smoked cannabis regularly and had a pre-existing risk of psychosis, 50 per cent developed psychotic symptoms over the period.


This was twice the rate among those who did not use cannabis and more than three times higher than among those who were neither vulnerable nor took the drug.


Five previous studies have shown a link between cannabis and psychosis but this is the first to quantify the risk in psychologically vulnerable individuals.


International experts meeting in London today will discuss the evidence at a conference on cannabis and health organised by the Institute of Psychiatry.


Robin Murray, a professor of psychiatry at the institute, said the popularity of cannabis combined with its increasing strength and the earlier age at which people started smoking were a cause for concern.


Comparing the rising toll of mental illness caused by cannabis to the epidemic of heart disease, he said: "We know lack of exercise and obesity are precursors for heart attacks. Now we are learning the precursors of psychosis."


Cannabis is the third most popular recreational drug after alcohol and tobacco, and Professor Murray said there was a question as to why more people were not psychotic. "It may be to do with how early you start.


The earlier it is, the greater the risk," he said.


Research in Australia shows that the average age at which people start smoking cannabis has come down since the 1970s from the early 20s to the mid-teens. In the Netherlands, it is 13 to 14, and in the UK it is unofficially estimated at 15 to 16.


Last week, figures showed that two in five 15-year-olds in the UK had tried cannabis - more than anywhere else in Europe. Zerrin Atakan of the National Psychosis Unit at the Maudsley hospital in south London said that the earlier people started using cannabis the more likely they were to become dependent on it. "If you smoke cannabis before 17, imaging studies show structural changes in the brain."


Studies of pregnant women who smoked cannabis showed changes in the brains of their children in later life, she said.


For the study, in the online version of the British Medical Journal, Jim van Os of Maastricht University and colleagues followed 2,437 young people from Germany.


Marjorie Wallace, the chief executive of the mental health charity Sane, said: "Britain's position as the cannabis capital of Europe could have hidden and disturbing consequences."


HEALTH BENEFITS


* Cannabis has been called the "aspirin" of the 21st century with evidence that its compounds may protect the brain against the effects of ageing.


* The world's largest study of the medical effects of cannabis reported in November last year that it could reduce pain and improve the lives of people with multiple sclerosis.


* Like alcohol, in moderation the drug promotes relaxation and enjoyment which are beneficial for human health.


HEALTH RISKS


* Regular cannabis smoking is associated with an increased risk of schizophrenia and depression.


* Up to 80 per cent of new cases of psychosis seen in psychiatric hospitals are triggered by cannabis abuse.


* Smoking three joints a day causes the same damage to the lungs as 20 cigarettes.


* The drug distorts perception, affects short-term memory and may cause hallucinations.


* Habitual users suffer from de-motivation.