Cannabis and schizophrenia link blurs further

The New Scientist

Can smoking pot make you potty? Even as the UK government mulls over evidence that cannabis can cause mental health problems, a new study suggests the link may be hazier than thought.

Last year, the UK downgraded cannabis to "class C", on a par with steroids and some prescription antidepressants. But in March, the government announced plans to review this decision. Some studies have suggested long-term cannabis use can increase your risk of developing schizophrenia (New Scientist, 26 March, p 44). Others have linked the drug to milder "schizotypal traits" that include odd, magical beliefs and social paranoia.

To test whether people who already have these traits are more likely to start using cannabis, Jason Schiffman at the University of Hawaii in Honolulu and his colleagues gave 189 students questionnaires about their cannabis use. The students were also asked if they had any schizotypal traits and if so when these traits first arose.

The results showed that the majority of people who'd recently used cannabis had schizotypal symptoms before using the drug (Psychiatry Research, vol 134, p 37). Schiffman admits that the limited study "leaves far more questions than answers" - for instance, it gives no clues as to why people with such traits might be attracted to cannabis.