Cannabis use linked to 40% rise in risk of schizophrenia

Smoking cannabis increases the risk of schizophrenia by at least 40% according to research which indicates that there are at least 800 people suffering serious psychosis in the UK after smoking the drug.

Mental health groups called on the government last night to issue fresh health warnings and launch an education campaign to advise teenagers that even light consumption of the drug could trigger long-term mental health problems. The findings came after a rush of ministers declared their cannabis-smoking pasts and an order from the prime minister for officials to consider whether the drug should be reclassified amid fears about its more potent "skunk" form. Last night the Home Office said the research would be considered in that review.

The study, an analysis published in the Lancet medical journal of previous research into the effects of the drug on tens of thousands of people, provides the most persuasive evidence to date that smoking cannabis can cause mental illness years after people have stopped using it.

The overall additional risk to cannabis smokers is small, but measurable. One in 100 of the general population have a chance of developing severe schizophrenia; that rises to 1.4 in 100 for people who have smoked cannabis.

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