You'd be crazy to believe this 'reefer madness' study

June 19, 2017
Heather de Rivera
C4 proteins, green, located at the synapses in a culture of human neurons. (Heather de Rivera/McCarroll Lab/Harvard via AP)
SOURCE: Heather de Rivera

‘Reefer madness’ is alive and well.

Writing in March in The American Journal of Addictions, a team of Greek researchers alleged to have scientific proof that smoking cannabis permanently damages the brain and drives people crazy.

Investigators performed psychiatric evaluations of 48 active and former cannabis consumers, 16 of whom were incarcerated in prison. Non-incarcerated participants were examined while they were acutely under the influence of pot. Those participants who were imprisoned were examined following several months of cannabis abstinence.

Authors alleged that some 85 percent of study’s subjects suffered from “organic brain dysfunction” — a condition that the authors failed to define and one that does not readily appear in the conventional medical literature. Researchers further claimed that more than half of the participants reported suffering from “delusions” and exhibited paranoia. Among the study’s imprisoned participants, researchers claimed that several similarly suffered from delusions, hallucinations, and supposed brain abnormalities — effects that the authors unquestioningly attributed to the participants’ past use of cannabis rather than from other potentially confounding variables, such as the existence of a pre-existing mental illness or the psychological and emotional stress associated with serving time in prison.

At no point in their study did authors address any potential limitations of their methods. (Most scientific research papers try to cite limitations.) Nor did they provide information on whether the participants possessed a family history or diagnosis of mental illness. (Known as confounding factors.) Study volunteers were also never subjected to any type of brain imaging examination, like a functional MRI. Finally, at no time did the study’s authors provide any substantive evidence as to why they believed that their findings, based upon an unusually small and unique sample size, ought to be extrapolated to the cannabis community at large — most of whom never report the sort of experiences alleged by the study’s participants. (That's known as generalizability.)

Nonetheless, authors opined, “We provide evidence that chronic and heavy cannabis abuse results in long-lasting brain dysfunction in all users and in long-lasting schizophrenia-like psychotic symptoms in more than half of all users.”

Reefer Madness

A frame from the iconic 1936 propaganda film Reefer Madness

Or not.

Allegations that smoking pot makes you crazy have can trace their origins back over a century. But the scientific literature has repeatedly failed to validated these claims, and empirical data — over one in two US adults self-report having experimented with the herb, the overwhelmingly majority of whom have suffered little if any ill psychological effects — further disputes this contention. Case in point: people are no more likely to be psychotic in Canada or the United States (two nations where large percentages of citizens use cannabis) than they are in Sweden or Japan (where self-reported marijuana use is extremely low). Even after the enormous popularity of cannabis in the1960s and 1970s, rates of psychotic disorders didn't increase among the general population. Ditto the 1990s, a period of time where cannabis use rose but incidences of schizophrenia and psychoses remained stable or declined.

Do some individuals with psychiatric disorders smoke pot? Of course. But according to a 2016 literature review, this association exists because many individuals predisposed to psychosis are simply more likely to experiment with weed at an early age as compared to those who are not. “Evidence reviewed here suggests that cannabis does not in itself cause a psychosis disorder,” researchers concluded. “Rather, the evidence leads us to conclude that both early use and heavy use of cannabis are more likely in individuals with a vulnerability to psychosis.”

Moreover, other studies find that a good number of these patients turn to cannabis in an effort to self-medicate the symptoms of their illness. According to a 2005 study published in the journal Addiction, the advent of psychotic symptoms increases the likelihood of becoming a pot smoker almost two-fold, and other research indicates that constituents in the plant, such as cannabidiol, hold promise as a potential treatment for symptoms of psychosis, paranoia, and schizophrenia.

Modern science further rebuts the allegation that pot permanently damages the brain. Longitudinal studies of adolescent twins find no attributable differences in IQ in marijuana users versus abstainers and dismiss the notion that cannabis exposure possesses neurotoxic effects.

Brain imaging data also counters this claim. Specifically, a 2015 study published in the Journal of Neuroscience reported on brain morphology in both daily adult and adolescent cannabis users compared to non-users, with a particular focus on whether any differences were identifiable in the nucleus accumbens, amygdala, hippocampus, and the cerebellum. They reported "no statistically significant differences ... between daily users and nonusers on volume or shape in the regions of interest" after controlling for participants' use of alcohol.

"[T]he 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," researchers concluded. "[I]t seems unlikely that marijuana use has the same level of long-term deleterious effects on brain morphology as [do] other drugs like alcohol. … The press may not cite studies that do not find sensational effects, but these studies are still extremely important."

And there lies the rub. Sensational claims about cannabis’ supposed deleterious health effects typically receive prominent press coverage and go largely unchallenged in the media. Conversely, scientific refutations of these allegations often receive little if any mainstream attention. As a result, reefer madness not only survives, but continues to thrive, particularly in the minds of those who steadfastly refuse to separate cannabis fact from fiction.

Paul Armentano is the Deputy Director of the National Organization for the Reform of Marijuana Laws (NORML) and is the co-author of the book Marijuana Is Safer: So Why Are We Driving People to Drink (Chelsea Green Publishing, 2013).