Psychotic illness appears to begin at younger age among those who use cannabis

February 7, 2011

A new study has provided the first conclusive evidence that cannabis use significantly hastens the onset of psychotic illnesses during the critical years of brain development - with possible life-long consequences.

Cannabis use appears to be associated with an earlier onset of psychotic illness, according to a meta-analysis of previously published studies posted online today that will appear in the June print issue of Archives of General Psychiatry.

More than 16 million Americans use cannabis on a regular basis, most of whom began using this and other drugs during their teenage years, according to background information in the article. "There is little doubt about the existence of an association between substance use and . National mental health surveys have repeatedly found more , especially cannabis use, among people with a diagnosis of a ," the authors write.

Matthew Large, B.Sc.(Med.), M.B.B.S., F.R.A.N.Z.C.P., of University of New South Wales and Prince of Wales Hospital, New South Wales, Australia, and colleagues identified 83 studies involving 8,167 participants who used cannabis or other substances and 14,352 individuals who did not. All of the studies compared the age at onset of psychosis between those two groups.

The meta-analysis found that individuals who used cannabis developed psychosis about 2.7 years younger than those who did not use cannabis. Those who used any type of substance developed psychosis about two years younger, whereas the use of alcohol only was not associated with the age at onset of psychosis.

"A number of hypotheses have been proposed to explain the association between cannabis use and , including the following: (1) that cannabis use is a causal factor for schizophrenia; (2) that cannabis use precipitates psychosis in vulnerable people; (3) that cannabis use exacerbates symptoms of schizophrenia; and (4) that people with schizophrenia are more likely to use cannabis," the authors write. The current findings support the view that cannabis use precipitates schizophrenia and other psychotic disorders, perhaps through an interaction between genetic and environmental disorders or by disrupting brain development, they note.

"The results of this study provide strong evidence that reducing cannabis use could delay or even prevent some cases of . Reducing the use of cannabis could be one of the few ways of altering the outcome of the illness because earlier onset of schizophrenia is associated with a worse prognosis and because other factors associated with age at onset, such as family history and sex, cannot be changed," the authors conclude. "The results of this study confirm the need for a renewed public health warning about the potential for cannabis use to bring on psychotic illness."

More information: Arch Gen Psychiatry. Published online February 7, 2011. doi:10.1001/archgenpsychiatry.2011.5

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4.5 / 5 (8) Feb 07, 2011
I'll take #4, Alex, until these bozos come up with ANY hard proof that there's a CAUSAL connection between cannabis and mental disease.

Aren't these the same people who note that mental diseases are much more prevalent today than in the Fifties?

Mental problems are so likely to be associated with cultural elements, which we are changing willy-nilly in our corporate consumer anxiety-ad-ridden society, that I don't see how anyone can sort out causality from association.

But the cannabis scare people in the tobacco and alcohol industries can be depended on to keep spreading the bad word about medical cannabis.
4.2 / 5 (5) Feb 08, 2011
Right on, ormondotvos!

Amazing how often "correlation" is substituted for causation in studies like this, and then makes it to print in what one supposes to be a peer-reviewed publication.

3.7 / 5 (3) Feb 08, 2011
it seems to me, that it as at lease AS likely that people who are prone to psychosis find that pot use ameliorates their symptoms and that they self medicate.

There is also little doubt that such illnesses are at least as often caused by environment and nurture as by nature.

I'd like to know who funded this study, and whether or not it's peer reviewed yet.
not rated yet Feb 08, 2011
The pot-crowd is not gonna like this...

alcohol only was not associated with the age at onset of psychosis.

can't use the "Alcohol is worse" line here...

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