REEFER MADNESS

Studies have suggested that as many as 1 in 4 cannabis users may be
genetically at risk for developing schizophrenia or a related
psychotic disorder. Now, a new study reveals all users are at risk.[1]

Given recent United Nations' statistics citing Canada as the
industrial world's leading consumer of cannabis, this news should set
alarm bells ringing. After all, a leading role in cannabis
consumption sets the stage for a leading role in psychotic disorders.
Instead, Canada's mainstream media responded in chorus from The Happy
Hippy Hymn Book, failing to notice that it is 10 years out of date.

"Legalizing pot makes sense," intoned a National Post editorial
earlier this summer, while a Globe and Mail article entitled "The
True North Stoned and Free" giggled about Canada's "little pot habit."

Schizophrenia, a severe form of psychosis, is a brain disorder that
typically produces delusions, hallucinations, paranoia, disturbances
in problem solving, memory and concentration, along with depressed
mood, anxiety and social withdrawal. Its causes are not fully
understood though environmental stressors (e.g., childhood trauma,
neglect) are thought to interact with genes to produce disruptions in
brain chemistry. Longitudinal and other studies demonstrate that
cannabis, at potencies much greater than 1960s' varieties, is one of
those stressors and that with their rapidly developing brains, the
young are particularly vulnerable to developing psychosis later in
life. The younger the user and the higher the potency of marijuana's
active ingredient, tetrahydrocannibol, the greater the risk.

In 2005, I interviewed the pre-eminent authority on marijuana and
psychosis, Professor Robin M. Murray. The Dunedin Birth Cohort Study,
in which he had participated, and which involved over 1037
participants from Dunedin, New Zealand, over 3 decades, had just been
published.[2] Murray explained how genes and marijuana could interact
to increase risk of developing psychosis. The
catechol-O-methyltransferase (COMT) gene, consisting of a MET
("normal") type and a VAL ("abnormal") type, metabolizes dopamine, a
brain chemical that produces the "highs" characteristic of drug and
alcohol use. A MET/VAL mixture increases risk 2-fold. A VAL/VAL
mixture increases risk 10 times. A quarter of the population is
VAL/VAL, he later explained during an interview entitled "Cannabis
and our genes" with BBC TV's Panorama.

Lead and co-author of countless studies as well as co-editor of
Marijuana and Madness, Murray is head of the Division of
Psychological Medicine and professor of psychiatry at King's College
Institute of Psychiatry in London. He has been a vocal critic of
British government policy that ignores the mental health issues
associated with marijuana use. In May, the Institute organized its
second conference on cannabis and mental health.

According to a recent study, 14% of British patients with
schizophrenia could have avoided the illness if they had not used
cannabis.[1] This meta-analysis also reveals that while the issue of
whether cannabis causes psychosis remains unclear, the risk of
developing psychosis from cannabis use by the general population,
irrespective of age or genes, is 41%. For heavy users - defined as
daily or weekly - the risk is in the range of 50% to 200%.

In 2004, the Canadian Addiction Survey found that 22% of all male and
10% of all female respondents aged 15-24 use cannabis on a weekly or
daily basis.

However you approach the math, it adds up to a disturbing result.

The news isn't all bad. Canada's marijuana decriminalization bill was
withdrawn in 2005, and now Health Minister Tony Clement is launching
an anti-drug campaign. For the medical and other communities,
however, the work is just beginning. Lobbying governments, informing
the media, gathering relevant Canadian data and educating families
are only a small part of what needs to be done. "Experts are now
agreed on the connection between cannabis and psychosis," Professor
Murray told USA Today. "What we need now is for 14-year-olds to know it."

FOOTNOTES

Margret Kopala writes columns for the Ottawa Citizen.

Have you got an opinion about this article? Post your views at
cmaj.ca. Potential Salon contributors are welcome to send a query to
salon@cma.ca

REFERENCES

1. Moore THM, Zammit S, Lingford-Hughes A, et al. Cannabis use and
risk of psychotic or affective mental health outcomes: a systematic
review. Lancet 2007;370:319-28.

2. Caspi A, Moffitt T E, Cannon M, et al. Moderation of the effect of
adolescent-onset cannabis use on adult psychosis by a functional
polymorphism in the catechol-O-methyltransferase gene: Longitudinal
evidence of a gene X environment interaction. Biol Psychiatry 2005;57:1117-27.