Is teen pot use really associated with long-lasting, adverse effects on memory and an increased risk of schizophrenia? The conventional media says so. But a closer examination of the scientific literature reveals that it is the mainstream media, not cannabis consumers, who are suffering from memory loss.

Marijuana Use and Cognition

Claims that marijuana consumption causes permanent damage to the brain and cognitive skills are hardly new. In fact, such claims have remained pervasive since the very inception of cannabis prohibition. Yet there exists little scientific data to support these persistent allegations.

For example, a comprehensive review published in 2003 in the Journal of the International Neuropsychological Society assessed effects of cannabis on neurocognitive performance in nearly a dozen published studies, involving over 1,000 test subjects. Authors reported: “In conclusion, our meta-analysis of studies that have attempted to address the question of longer term neurocognitive disturbance in moderate and heavy cannabis users has failed to demonstrate a substantial, systematic, and detrimental effect of cannabis use on neuropsychological performance. It was surprising to find such few and small effects given that most of the potential biases inherent in our analyses actually increased the likelihood of finding a cannabis effect.”

A 2012 meta-analysis of 33 separate studies by researchers at the University of Central Florida Department of Psychology similarly reported that moderate to heavy marijuana consumers failed to experience “enduring negative effects” associated with cognition. Writing in the journal Experimental and Clinical Psychopharmacology, investigators reported that cannabis chronic consumption may be associated with "small" effects on neurocognitive abilities for limited periods of time lasting beyond the immediate hours of intoxication, but they found "no evidence of lasting effects on cognitive performance due to cannabis use" in subjects whose abstention period was at least 25 days. Authors concluded: "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."

Marijuana Use and Schizophrenia

The mainstream media has long been fixated on the allegation that smoking pot will make you crazy. (For perspective, read my 2011 HIGH TIMES feature, "Don’t Blame the Reefer,") So it was hardly unusual to see mainstream news outlets this week run with headlines implying that marijuana use may increase one’s risk of schizophrenia. Yet, scientific research establishing such a link remains tenuous. In fact, in the days prior to this week’s media frenzy, researchers at Harvard University released a study soundly rebutting this allegation.

Writing in the peer-reviewed journal Schizophrenia Research, investigators compared the family histories of 108 schizophrenia patients and 171 individuals without schizophrenia to assess whether youth cannabis consumption was an independent factor in developing the disorder. Researchers reported that a family history of schizophrenia increased the risk of developing the disease, regardless of whether or not subjects consumed cannabis as adolescents. They concluded: “The results of the current study, both when analyzed using morbid risk and family frequency calculations, suggest that having an increased familial risk for schizophrenia is the underlying basis for schizophrenia in these samples and not the cannabis use. While cannabis may have an effect on the age of onset of schizophrenia it is unlikely to be the cause of illness.”

The finding was hardly a surprise. After all, worldwide rates of schizophrenia have largely remained stable for decades despite dramatic changes in per capita marijuana use. In countries with marked spikes in cannabis use, researchers have failed to report parallel increase in incidences of schizophrenia or psychotic disorders.

Further, studies indicate that specific cannabinoids, such as cannabidiol (CBD), may even be efficacious in treating symptoms of the disease. According to a review published in the November issue of the journal Neuropsychopharmacology, “CBD has some potential as an antipsychotic treatment. … Given the high tolerability and superior cost-effectiveness, CBD may prove to be an attractive alternative to current antipsychotic treatment.” More notably, a 2012 double-blind, randomized placebo-controlled trial assessing CBD versus the prescription anti-psychotic drug amisulpride in 42 subjects with schizophrenia and acute paranoia concluded that two substances provided similar levels of improvement, but that cannabidiol did so with far fewer adverse side effects.



The Bottom Line

Societal concerns regarding cannabis’ potential impact on the adolescent brain and its possible association with psychiatric illnesses arguably warrant further study. However, such concerns — even if confirmed by sound clinical science — are not persuasive justifications for continuing cannabis criminalization. Just the opposite is true. There are numerous adverse health consequences associated with alcohol, tobacco and prescription drugs, all of which are far more dangerous and costlier to society than cannabis. It is precisely because of these consequences that these products are legally regulated and their consumption is restricted to specified consumers and settings. Further, abuse of these substances is discouraged and science-based education campaigns regarding these products’ potential risks are prevalent. So isn’t it time we once and for all ended our nearly century-long love affair with reefer madness and applied these same common sense principles to cannabis?