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Marijuana Use Associated with Earlier Onset of Psychotic Illness

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Marijuana Use Common Across the US

More than 16 million Americans use marijuana 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 psychotic illness. National mental health surveys have repeatedly found more substance use, especially marijuana use, among people with a diagnosis of a psychotic disorder,” according to the study authors.

Marijuana Mental Health Study

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 marijuana (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 marijuana users developed psychosis about 2.7 years younger than those who did not use marijuana.  Those who used any type of substance developed psychosis about two years younger, whereas the alcohol use was not associated with the age at onset of psychosis.

“A number of hypotheses have been proposed to explain the association between marijuana use and schizophrenia, including the following: (1) that marijuana (cannabis) use is a causal factor for schizophrenia; (2) that marijuana (cannabis) use precipitates psychosis in vulnerable people; (3) that marijuana (cannabis) use exacerbates symptoms of schizophrenia; and (4) that people with schizophrenia are more likely to use marijuana (cannabis),” the authors write. The current findings support the view that marijuana (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 regarding marijuana use provide strong evidence that reducing marijuana use could delay or even prevent some cases of psychosis. Reducing the use of marijuana could be one of the few ways of altering the outcome of mental 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 regarding  marijuana use and mental illness confirm the need for a renewed public health warning about the potential for marijuana use to bring on psychotic illness.”

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

Last modified on Sunday, 24 July 2011 15:58
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