CANNABIS increases the risk of schizophrenia or depression, new studies have shown.

A long-term follow-up of a 1960s study of Swedish army recruits shows that, broadly, using cannabis doubles the risk of schizophrenia, and using it 50 times increases the risk about sevenfold. The link persisted after correcting for cigarette smoking, social background and the use of other drugs (Nigel Hawkes writes).

A New Zealand study shows that 10 per cent of those who used cannabis by the age of 15 developed schizophrenia, compared with 3 per cent of non-users. The authors of the report, from King’s College London and the University of Dunedin, say: “Our findings suggest that cannabis use among psychologically vulnerable adolescents should be strongly discouraged.”

An Australian study of 1,600 students from 44 secondary schools found that frequent cannabis use was linked to later depression and anxiety, particularly in girls. Daily use increased the risk fivefold. Weekly use doubled the risk.The results are all published in the British Medical Journal.

Marjorie Wallace, chief executive of the mental health charity Sane, said: “Recent research papers are increasingly confirming Sane’s extreme concerns about the use of cannabis.”

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