 | NORML News: Schizophrenia link is reefer madness all over again |
 By Stephen McIntyre.
The British Medical Journal recently featured an article discussing a University of Otago study which claimed a link between cannabis use and schizophrenia.
The Dunedin researchers claimed that there was a causal link between the two, and that cannabis smoking actually increased the risk of an individual becoming schizophrenic.
Whether cannabis causes mental illness is a debate that can be traced back to 1894, when the Indian Hemp Commission concluded that overindulgence in the drug could only be regarded as a symptom, not a cause, of predisposition to insanity.
In their book ‘Marijuana Myths, Marijuana Facts’, Doctors Lynn Zimmer and John Morgan point out that while claims that marijuana causes permanent mental illness reappear consistently, “there is no scientific evidence that marijuana causes psychological damage or mental illness in either teenagers or adults”.
They note that studies often contradict each other, although the overwhelming body of evidence falls on the side making no causal link between cannabis and mental illness. A Swedish study (Allebeck, et al, 1993) found that cannabis use most commonly preceded the appearance of schizophrenia. However, others ( Hall, et al, 1994; Thornicroft, et al, 1990; Hollister, et al, 1986) found that marijuana use was much more likely to follow the onset of psychiatric symptoms eliminating it as a causal factor in those cases.
The University of Otago study found that of the 15-year-olds who admitted using cannabis, ten percent developed psychotic symptoms by age 26. Of those who had not used cannabis at all, or said they started later, only three percent developed a form of psychosis. There are weaknesses to any self-reported study, and it’s yet to be revealed how researchers controlled for other factors that cause schizophrenia.
Schizophrenics tend to try cannabis more than other people. But that doesn’t mean cannabis causes schizophrenia. If it did, then after decades of increasing use there would be rises in cases of schizophrenia. But there aren’t! Indeed, the Health Funding Authority told the Health Select Committee that the incidence of schizophrenia declined during a period in which cannabis use increased among young adults.
The Committee, in its 1998 NZ Mental Health Effects of Cannabis report, said that “the negative mental health impact of cannabis appears to have been overstated.”
“If cannabis does cause harm to a small proportion of users then it is preferable that those people have good access to treatment without fear of stigmatisation and discrimination”, said the committee.
“Those who develop problems are less likely to seek help because they use an illegal substance, and may spiral in alienation, antisocial behaviour [and] mental illness.”
Their recommendation was that existing cannabis policy be reviewed and the legal status of cannabis reconsidered.
Under prohibition, communities have no say where, when or to whom cannabis is sold. Prohibition puts that role into the hands of organised criminals, and, as a result, the health of our whole society suffers. Regulating and controlling cannabis to minimise harms, especially amongst young people - that’s what this debate should really be about.
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