Teens warned pot smoking could lead to schizophrenia

(From The Province: August 28, 2006)

Cannabis use can trigger schizophrenia in people already vulnerable to the illness - and this fact should shape marijuana policy, argue two psychiatric epidemiologists. The problem is that the vulnerable population - mostly teenagers - generally aren't eager to absorb the message.

Australian epidemiologists Louisa Degenhardt and Wayne Hall concluded that using marijuana can precipitate schizophrenia in users who have a personal or family history of schizophrenia.

One 15-year study of 50,000 young people in Sweden, for example, found that those who had tried marijuana by the time they were 18 were 2.4 times more likely to receive a diagnosis of schizophrenia. The Swedish researchers concluded that 13 per cent of schizophrenia cases could be averted if all cannabis use was prevented.

Other studies suggested that subjects who used marijuana in their early teens were more likely to be diagnosed with schizophrenia by their mid-20s.

In Australia - where marijuana use is heavy among teens - it's not uncommon for 20 to 30 per cent of new episodes of schizophrenia to be among patients who use marijuana daily or almost daily.

Wende Wood, a psychiatric pharmacist at the Toronto-based Centre for Addiction and Mental Health said people who want to smoke marijuana should wait until they are at least 25 - the human brain had developed fully by that time, and if schizophrenia is present, it has usually already become apparent.