EDITOR: | October 12th, 2015

Marijuana effects: Debunking political rhetoric

| October 12, 2015 | No Comments

Stephen-HarperOn Saturday October 3, 2015 Canadian Prime Minister Stephen Harper stated to a cheering partisan audience: “Tobacco is a product that does a lot of damage. Marijuana is infinitely worse and it’s something that we do not want to encourage.”

He added, “There’s just overwhelming and growing scientific and medical evidence about the bad long-term effects of marijuana,” not providing examples or citations.

The British peer-reviewed journal Lancet published a study titled “Drug Harms in the UK: A Multicriteria Decision Analysis” on Nov. 1, 2010 which calculated the harm factors of 20 drugs from alcohol to marijuana to tobacco based on harm. The study calculated harm caused to individuals as for example dependence, mortality, and impairment of mental functioning which were lumped under “harm to users,” as well as “harm to others” as for example crime, environmental damage, and international damage. What makes this experimental approach useful is that these factors were quantitatively consolidated into life cycle measurements.

The study concluded that alcohol was the most harmful drug overall (72 out of 100 points), followed by heroin (55 out of a maximum of 100 points), and crack cocaine (54 out of 100 points). The most harmful drugs to users were crack cocaine, heroin, and methamphetamine (scores of 37, 34, and 32, respectively), whereas alcohol, heroin, and crack cocaine were the most harmful to others (scores of 46, 21, and 17, respectively). Marijuana had an overall harm score of 20 points, putting it in eighth place behind amphetamines and before liquid ecstasy.

In the same study, tobacco scored 26, 6 points higher than marijuana.

A review article in the New England Journal of Medicine titled “Adverse Health Effects of marijuana use published in June 2014 9% of people who experiment with marijuana will become addicted.

The World Health Organization reports that 50% of those who start smoking tobacco in the adolescent years continue to smoke for 15 to 20 years.

How about alcohol? The NHS in the UK estimates that around 9% of men in the UK and 4% of UK women show signs of alcohol dependence (sometimes known as ‘alcoholism’).

Still this does not mean that marijuana is innocuous but it means that Mr. Harper is undoubtedly wrong about marijuana being infinitely more dangerous than alcohol and tobacco.

I’m excerpting the abstract of a 2015 study titled Daily Marijuana Use Is Not Associated with Brain Morphometric Measures in Adolescents or Adults publishing in the Journal of Neuroscience. I’m excerpting the abstract here because of the significant of those findings:

Recent research has suggested that marijuana use is associated with volumetric and shape differences in subcortical structures, including the nucleus accumbens and amygdala, in a dose-dependent fashion. Replication of such results in well controlled studies is essential to clarify the effects of marijuana. To that end, this retrospective study examined brain morphology in a sample of adult daily marijuana users (n = 29) versus nonusers (n = 29) and a sample of adolescent daily users (n = 50) versus nonusers (n = 50). Groups were matched on a critical confounding variable, alcohol use, to a far greater degree than in previously published studies. We acquired high-resolution MRI scans, and investigated group differences in gray matter using voxel-based morphometry, surface-based morphometry, and shape analysis in structures suggested to be associated with marijuana use, as follows: the nucleus accumbens, amygdala, hippocampus, and cerebellum. No statistically significant differences were found between daily users and nonusers on volume or shape in the regions of interest. Effect sizes suggest that the failure to find differences was not due to a lack of statistical power, but rather was due to the lack of even a modest effect. In sum, the results indicate that, when carefully controlling for alcohol use, gender, age, and other variables, there is no association between marijuana use and standard volumetric or shape measurements of subcortical structures.

While marijuana is not infinitely more dangerous than alcohol and tobacco, we must acknowledge that marijuana smoking is not innocuous, like everything else. For example, a Swedish study showed that incidence of lung cancer is greater in lifetime smokers of marijuana as compared to controls.

Dr. Luc Duchesne


Dr. Luc C. Duchesne is a Speaker and Author with a PhD in Biochemistry. With three decades of scientific and business experience, he has published ... <Read more about Dr. Luc Duchesne>

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