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Marijuana & Schizophrenia Study: Kids Shouldn’t Smoke

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By "Radical" Russ Belville

The media have once again trumpeted the headlines of a link between marijuana use and schizophrenia and other psychoses.  As we’ve reported numerous times, the rates for schizophrenia and psychoses seem to stay constant at about 1% of the population, regardless of how many people consume cannabis and how much they consume.

This latest meta-analysis, however, claims cannabis use is causing those 1% who would become schizophrenic to fall victim to their mental illness sooner and to suffer the effects of psychosis to a greater extent:

We found that the use of cannabis and other illicit substances was associated with an earlier age at onset of psychotic disorders. In contrast, alcohol use alone did not appear to be significantly associated with a younger age at onset of psychosis.

The results of this systematic review and meta-analysis represent strong scientific evidence for an association between substance use, particularly the use of cannabis, and an earlier age at onset of psychotic illnesses.

The results of this study provide strong evidence that reducing cannabis use could delay or even prevent some cases of psychosis. 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.

Building on several decades of research, this finding is an important breakthrough in our understanding of the relationship between cannabis use and psychosis. It raises the question of whether those substance users would still have gone on to develop psychosis a few years later. However, even if the onset of psychosis were inevitable, an extra 2 or 3 years of psychosis-free functioning could allow many patients to achieve the important developmental milestones of late adolescence and early adulthood that could lower the long-term disability arising from psychotic disorders. 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.

The lead researcher says it bluntly – “marijuana is a cause of schizophrenia” – and makes a strong denunciation of the idea that schizophrenics are self-medicating with cannabis:

(WebMD) “It is increasingly clear that marijuana is a cause of schizophrenia, and that the schizophrenia caused by cannabis starts earlier than schizophrenia with other causes,” study researcher Matthew Large of Prince of Wales Hospital in New South Wales, Australia, says in an email. “Young people are at particular risk.”

“There is not so much evidence for the widely held view those patients self-medicate with marijuana,” he says. “Marijuana smoking almost always comes before psychosis and few patients with psychosis start smoking [marijuana] for the first time.”

More than 80% of the patients in the study had schizophrenia, but there were some other forms of psychosis identified among marijuana users. “The picture looked similar irrespective of the type of psychosis,” Large says.

We’ll talk to Dr. Mitch Earleywine about this on our Cannabis Science segment on the Wed. Feb. 9 NORML SHOW LIVE, but I can tell you this study confirms something NORML has always believed – children and people with a propensity to mental illness should not be smoking marijuana.

However, this study is by no means an argument for continued marijuana prohibition.  Cigarettes and alcohol are harmful to children as well as adults, but we understand that education has reduced the harm from those substances and prohibition of the latter was a dismal failure that created violence and corruption.    The system we have now guarantees that kids find it easy to get marijuana and that when they do they’re interacting with a criminal market.

I’m still skeptical.  If these are folks that were going to get schizophrenia anyway and we know that the rates of schizophrenia stay fairly constant, then this study’s hypothesis should mean that we’d see the median age of onset of schizophrenia declining in the populations with greater cannabis use among youth.  I don’t know how to test that theory… again, we’ll ask Dr. Mitch.


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