Two recently published studies might have put the last couple of nails in the coffin on the idea that smoking cannabis shrinks the brain, but the National Institute on Alcohol Abuse and Alcoholism (NIAAA) quickly jumped in to say it’s still too early to declare the herb safe enough for legalization.
David Goldman, M.D. of the NIAAA wrote an editorial concerning the two studies saying “it would be wrong to conclude that it is safe to use cannabis or… to conclude that it would be safe for people with the right genetic makeup or women, in particular, to use cannabis.” While this is the quote most of the mainstream media has fixated its gaze on, what does the latest science actually tell us about the brains of people who use cannabis?
The first study published by the Washington University in St Louis Missouri compared brain volumes between siblings who smoked or didn’t smoke weed. Cannabis users overall had slightly smaller left amygdalas (a region involved in memory and decision making) and right ventral striata (a region involved in motivation, planning and reward perception), but the differences “were within normal variation.” However, if only one sibling in a pair ever smoked weed, and the other one had never, both of them still had smaller brain volumes. Therefore they concluded that differences in amygdala volumes in cannabis users could be attributed to genetic or environmental factors, with little reason to say cannabis shrunk amygdalas. The reason for smaller ventral striatum volumes was unclear, but genetic and environmental factors could still be at play. As the largest study of its kind so far, its conclusions hold a great deal of water.
The second study, authored by Leon French, PhD of the Rotman Research Institute in Ontario, Canada, looked into the relationship between the cerebral cortex (a large part of the brain that deals with complex thought), cannabis use and whether genetic risk factor for schizophrenia in adolescents has any involvement. Researchers have previously shown that schizophrenia patients can have smaller cerebral cortices, and those people may be genetically predisposed to this mental illness. Genes can also influence a person’s likelihood of becoming addicted to nicotine, alcohol or cocaine, but the genetic association to so-called “cannabis addiction” is quite loose.
Leon French’s study found that only adolescent males at high risk for schizophrenia (based on genetic testing) had smaller cerebral cortex volumes after years of cannabis use. In low-risk males and in all females (both low- and high-risk for schizophrenia), there was no association between smaller brains and cannabis use. They concluded “cannabis use in early adolescence moderates the association between the genetic risk for schizophrenia and cortical maturation among male individuals.” Cannabis prohibitionists have made the claim that smoking reefer can cause schizophrenia but this myth has since been dispelled by modern science. Individuals predisposed to the illness may be more likely to smoke weed due to genetic or environmental causes, and this latest research shows they probably shouldn't.
These two studies don’t conclude cannabis shrinks brains or is unsafe, but David Goldman from the National Institute of Alcohol Abuse and Alcoholism still thinks we should be weary of the Devil’s Weed. Don’t believe the hype about marijuana shrinking your brain. The Reefer Madness hasn’t stopped; the government still tries to warp the public’s view on hard science in an effort to make people think a simple herb is a dangerous drug. Nicotine and alcohol have been proven to cause brain atrophy and shrinkage yet they remain legal in most of the world. Cannabis may not be perfect but it is undoubtedly the safest recreational drug in existence, and competes with many prescription drugs for its safety as well as medical value.