Does pot smoking make people crazy, or do lots of crazy people smoke pot? That’s the question raised by the findings of a just published study sponsored by the Canadian Centre for Addiction and Mental Health.
It’s hardly the first time that society has pondered this issue. Allegations of the cannabis plant triggering violent or psychotic behavior was a basis for the federal government successful “reefer madness” campaign in the 1930s. Hindsight, of course, later showed these claims to be categorically false. Nevertheless, over the past decade, concerns regarding marijuana’s role as a potential underlying component in various forms of mental illness, predictably schizophrenia, have once again surfaced, largely fueled by prohibitionists forces in Britain and in the US. As in the past, however, the hard science in support of such claims remains largely suspicious. Despite a spat of recently published peer-reviewed papers on the subject, investigators findings remain for the most part contradictory, raising far more questions than they answer.
Such is the case with the latest data compiled by Canadian scientists and published online in the journal Scientific Psychiatry. Investigators at the Centre for Addiction and Mental Health and the University of Toronto analyzed data gathered from face-to-face interviews with a nationally representative cross-section of over 43,000 US respondents ages 18 and older. Using structured questionnaires, the researchers assessed the association between cannabis use and the prevalence of various mental illnesses, including depression, anxiety and personality disorders.
“The odds ratio for cannabis use among individuals with 12 month mental illness versus respondents without any mental illnesses was 2.5,” the researchers concluded that the plant was “particularly associated with bipolar disorder, substance abuse disorders and specific personality disorders.”
But is association… equivalent to causation?
Dr. Mitch Earleywine, author of the book understanding marijuana: a new look at the scientific evidence and a member of NORML’s Board of Directors warns that patients with mental illness typically consume various psychotropic substances at rates far greater than those of the general population. Indeed, a 2009 population-based assessment of US and Australian respondents reported that patients with affective disorders were more than twice as likely to smoke cigarettes than were adults with no prior history of such illness – but no one is suggesting that puffing Marlboros triggers mental instability.
Reviews of cannabis use data from around the globe indicate that pot doesn’t do so either. For example, people are no more likely to be diagnosed with mental illness in the US and Canada – two nations with among the highest rates of marijuana use – then they are in Sweden or Japan, where self-reported marijuana use is comparatively low.
Furthermore, the increased popularity of cannabis in recent decades, both here and abroad, has not been associated with a parallel increase in the prevalence of mental disorders. Specifically, a 2009 study authored by researchers at Keele University Medical School in Britain compared trends in marijuana use and incidences of serious mental illness in the United Kingdom from 1996 to 2005. Investigators found that the “incidence and prevalence of schizophrenia and psychosis were either stable or declining” during this period, even as the use of cannabis among the general populace was rising.
So if cannabis use isn’t the cause of mental illness, why do so many people with psychiatric disorders report using it? The likely explanation for this association, says Dr. Earleywine, is that many patients are simply self-medicating with cannabis. Cannabis is well known to be a safe and effective mood enhancer, and can have dial, a key component of the plant, possesses documented antianxiety properties. A 2012 study published in the scientific journal Psychiatry Research reported that bipolar patients with a history of marijuana use performed better on a series of narrow conductive tests than bipolar patients with no such history. Similar findings have been reported among patients with schizophrenia as well.
Ultimately, however, do reemerging claims about cannabis and its harmful effects on mental health will likely do little to stave off the increasing momentum of public sentiment in favor of the plants legalization and regulation. Unlike the scare tactics of the 1930s, which spurred calls for criminalization, today’s claims the cannabis use causes psychotic behavior appear to carry little weight with a voting public that’s become justifiably wary of pot prohibition.