Drugs

Why the Media's Fearmongering on Marijuana Effects on the Brain Is Faulty

A neuroimaging study of the brains of marijuana smokers caused unwarranted frenzy.

Photo Credit: Darren J. Bradley / Shutterstock.com

The mainstream media launched into a reefer mad frenzy this week after researchers from Harvard University in Boston and Northwestern University in Chicago published the results of a neuroimaging study assessing the brains of a small cohort of regular marijuana smokers and non-users. The brain scans identified various differences between the two groups in three aspects of brain morphometry: gray matter density, volume, and shape. These differences triggered dozens of high-profile media outlets to lose their collective minds. Here’s just a sample of the screaming headlines:

CNN: Casual marijuana use may damage your brain; Science Daily: More joints equal more damage; Financial Post: Study proves occasional marijuana use is mind altering; Time: Recreational pot use harmful to young people’s brains; Smoking cannabis will change you. That’s not a risk, its acertainty.

Just imagine how the media would have responded if the study in question had included more than 20 actual cases — or if the authors had actually bothered to assess its subjects for demonstrable deficits in cognitive performance. Yes, that’s right. Despite the sky-is-falling rhetoric and the shock claims of permanent brain damage, a careful review of the study and its findings reveals little, if any, cause for alarm.

So what did the study find? In truth, not a whole lot. 

Using high–resolution MRI imaging, scientists identified specific changes in particular regions of the brain that they inferred were likely due to marijuana exposure. (Since researchers only performed a single MRI session, they could not say definitively whether these changes were, in fact, caused by cannabis or whether they existed prior to subjects’ use of the plant.) Notably, however, these changes did not appear to be associated with any overt adverse effects in subjects’ actual cognition or behavior. (Separate studies assessing youth use of legal intoxicants, such as nicotine and alcohol,have also been associated with documented changes in brain structure. Ditto for caffeine intake in preclinical models. These findings have received far less media attention.)
 
Both the cases (20 marijuana users) and controls (20 nonusers) in the study were recruited from local universities, undermining the notion that the alleged ‘brain damaged potheads’ were any more academically challenged than their non-using peers. Further, as summarized by HealthDay: “Psychiatric interviews revealed that the pot smokers did not meet criteria for drug dependence. For example, marijuana use did not interfere with their studies, work or other activities, and they had not needed to increase the amount they used to get the same high.”
 
In other words, case subjects and controls appeared to function similarly in their professional and academic endeavors. 
 
That finding should hardly come as a surprise. Dozens of separate neurocognitive studies consisting of far larger sample sizes find no substantial, systematic effect of long-term, regular cannabis consumption on brain functioning once the users have abstained from the drug. As concluded in one recent meta-analysis of 33 such studies, published in the journal Experimental and Clinical Pharmacology: “As hypothesized, the meta-analysis conducted on studies evaluating users after at least 25 days of abstention found no residual effects on cognitive performance. ... These results fail to support the idea that heavy cannabis use may result in long-term, persistent effects on neuropsychological functioning.”
 
A separate review of nearly a dozen studies (involving a total of 623 cannabis users and 409 non- or minimal users) published in the Journal of the International Psychological Society similarly reported, “The results of our meta-analytic study failed to reveal a substantial, systematic effect of long-term, regular cannabis consumption on the neurocognitive functioning of users who were not acutely intoxicated.”
 
Moreover, other studies, though admittedly comprised of small sample sizes, have indicated that in some instances cannabis may actually protect the brain, particularly against the potentially damaging effects of alcohol.

This is not to say that consuming marijuana, particularly in heavy quantities, is not without potential risk to learning retention, short-term memory, and other potential cognitive skills—especially when it is consumed by young people whose brains are still developing. However, after decades of marijuana use by significant portions of the public (despite the plant’s prohibition), it is apparent that these associated potential risks are not so great as to warrant the continued arrest of some 700,000 Americans annually for possessing the plant. Nor do these potential risks justify marijuana’s present status as a schedule I controlled substance, a classification that equates the purported dangers of pot to be equal to those of heroin.

Such fear-mongering and sensationalism by the mainstream media in regards to the supposed harms of pot upon the brain are nothing new. It wasn’t long ago that the mainstream media was boldly claiming that cannabis use permanently lowered IQ, a finding that marijuana prohibitionists and anti-drug bureaucrats were happy to repeat ad nauseam.

Reported CBS News at the time, “Dr. Nora Volkow, director of the National Institute on Drug Abuse which helped fund the research, said the research was ‘the cleanest study I've ever read’ that looked long-term harm from marijuana use.”

Except it wasn’t. A separate analysis of the data, published only weeks later in the Proceedings of the National Academy of Sciences, acknowledged that the study’s authors failed to properly control for subjects’ socioeconomic status. It concluded, “A simulation of the confounding model reproduces the reported associations from the Dunedin cohort, suggesting that the causal effects estimated in Meier et al. are likely to be overestimates, and that the true effect in regards to marijuana’s potential effect on IQ) could be zero.”

Predictably, the mainstream media’s coverage of this refutation was nonexistent.
 
As a result, prohibitionists still continue to publically raise the disproven allegation that pot use lowers IQ as if it is fact. Most likely, those of us who advocate for saner marijuana policies will be similarly responding to these equally specious claims that cannabis causes brain damage for many years to come.

Paul Armentano is the deputy director of NORML (National Organization for the Reform of Marijuana Laws) and serves as a senior policy advisor for Freedom Leaf, Inc. He is the co-author of the book, Marijuana Is Safer: So Why Are We Driving People to Drink? (Chelsea Green, 2013).

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