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Longtime cannabis use may raise risk of psychosis

Young adults who are longtime pot smokers are more likely to have hallucinations, delusions, or to display signs of psychosis than short-term smokers or people who've never smoked marijuana.

The finding comes from a study of 3,801 young adults who were asked about their pot use and then evaluated to determine if they'd experienced "psychotic outcomes."

The study appears online in advance of print in the May issue of the Archives of General Psychiatry.

The findings showed that youths who had experienced hallucinations early in life were more likely to have used marijuana longer, and more frequently.

The researchers followed young people born between 1981 and 1984, up to age 21. They were asked about their use of cannabis.

Overall, 233 had at least one "positive" report for hallucination on their interviews, and 65 received a diagnosis of "non-affective psychosis," such as schizophrenia.

According to researcher John McGrath, Non-affective psychosis "is a broad category that includes schizophrenia and a handful of less common disorders like delusional disorder".

The study also shows that those who had at least six years since the first time they used marijuana were four times as likely to have high scores on an accepted measure of delusionary experiences.

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