ONE IN FOUR CANNABIS USERS
MAY BE AT RISK

Margret Kopala

August 30, 2007

SCIENTIFIC research suggests that as many as one in four cannabis users may be genetically at risk for developing schizophrenia or a related psychotic disorder.  Now, a new study published in The Lancet (1) reveals all users are at risk.

Given recent UN 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 main stream media responded as if someone had passed out The Happy Hippy Hymn Book that no one noticed is ten years out of date.

“Legalizing pot makes sense,” intoned a National Post editorial.  Comparing cannabis with alcohol and tobacco, it asked where’s the “health foot print of our love for the weed?”  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 (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 for developing psychosis later in life. The younger the user and the higher the potency of tetrahydrocannibol (THC): the greater the risk.

In 2005, I interviewed the pre-eminent authority on marijuana and psychosis, Professor Robin Murray, for the Ottawa Citizen. The Dunedin Birth Cohort Study in which he had participated and which involved over 1,000 adolescents at Dunedin, New Zealand had just been published. (2)   I learned how genes and marijuana could interact to increase risk of developing psychosis. The COMT gene, consisting of a MET type and a VAL type, metabolizes dopamine, a brain chemical that produces the ‘highs’ characteristic of drug and alcohol use. A MET/VAL mixture increases risk two fold. A VAL/VAL mixture increases risk ten times. Since a quarter of the population is VAL/VAL, a quarter is MET/MET and the rest a mixture, the assessment that 25% of youth are at risk is probably conservative. Lead and co-author of countless studies as well as co-editor of Marijuana and Madness, Robin M. Murray is Head of the Division of Psychological Medicine and Professor of Psychiatry at King’s College Institute of Psychiatry in London.  Here, he has been a vocal critic of British government policy that ignored the mental health issues associated with marijuana use. In May, the Institute organized its second conference on cannabis and mental health. The latest study from Britain indicates 14% of Britain’s schizophrenics could have avoided the illness if they had not used cannabis.  This meta-analysis, published in the July issue of The Lancet, 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 it on a weekly or daily basis.

Do the math.  The result isn’t pretty. For Canada, the news isn’t all bad.  Its 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, monitoring patients, 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.”

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Margret Kopala writes columns for the Ottawa Citizen. margret.kopala@sympatico.ca

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

2.  Caspi A, Moffitt T E. Cannon M, McClay J, 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. Biological Psychiatry 2005; 57:1117-27.