Some young people who smoke cannabis are at real risk of developing psychotic mental illness, according to a major study announced yesterday. The new survey of 2,500 young people aged 14 to 24 will be discussed at the start of an international conference today on cannabis and mental health convened by the Institute of Psychiatry in London.
It shows that regular cannabis smoking increased the risk of developing psychosis by 6% over four years. But there was a substantially greater impact on young people who had already been identified by psychiatrists as having the potential to become psychotic. Regular cannabis smoking raised their risk of developing psychotic mental illness by 25%.
The study aimed to answer a question that has been unsettling psychiatrists for some time. People with psychosis, whose symptoms include hallucinations, paranoia, hearing voices and a persecution complex, are more likely than not to have a marijuana habit. But doctors have not known whether they are smoking it for relief from their symptoms, or whether cannabis itself might be the problem.