Alex Berenson’s recent attempt to generate panic at the prospect that marijuana use may become legalized and normalized, with his book Tell Your Children: The Truth About Marijuana, Mental Illness, and Violence, even borrows its title from the camp 1930s propaganda film Reefer Madness. While not nearly as over-the-top as the film, Berenson certainly exaggerates suggestions that marijuana can cause psychosis.
Drawing on the 2017 report of the National Academy of Sciences, Engineering, and Medicine on “Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research,” he directs attention to its conclusion, in Chapter 12: “There is substantial evidence of a statistical association between cannabis use and the development of schizophrenia or other psychoses, with the highest risk among the most frequent users.” Berenson admits in a January 4 Wall Street Journal column based upon his book, “None of these studies prove that rising cannabis use has caused population-wide increases in psychosis or other mental illness, although they do offer suggestive evidence of a link.” Indeed. But correlation is not causation. And there is always the question of “which came first–the chicken or the egg?” Some schizophrenics might be using cannabis as a form of self-medication.
The NASEM report also notes, “There are a number of proposed explanations for why the comorbidity of substance abuse and mental health disorders exists.” One suggested explanation is “an overlap in predisposing risk factors (e.g., genetic vulnerability, environment) may contribute to the development of both substance abuse and a mental health disorder,” and indeed there are studies suggesting a genetic predisposition exists for some cannabis users to develop schizophrenia. There is also research showing an increased risk for the development of schizophrenia associated with heavy marijuana use where a family history of schizophrenia exists.
But it is also important to note that many countries saw stable or declining rates of psychosis between the 1960s and 1980s, a time when marijuana use in those countries increased dramatically. A 2003 Australian study found “no causal relationship” between cannabis use and schizophrenia, and a 2012 British study found rates of schizophrenia stable from 1950 to 2009, a time of greatly increased marijuana use.
And while there may be a correlation between schizophrenia and heavy marijuana use, the NASEM report stated, “cannabis use does not appear to increase the likelihood of developing depression, anxiety, and posttraumatic stress disorder.” Yet these are the most commonly cited “serious mental illnesses” that were found to be associated with heavy cannabis use among 18 to 25 year-olds in the National Survey on Drug Use and Health on which Berenson also relies to make his case.
Psychiatrists have long known that the majority of patients with substance abuse disorders have psychiatric comorbidities, which need to be addressed in concert with the treatment of the substance abuse disorder. What is not yet known is how much the substance abuse disorders are actually driven by the comorbidities.
No one is arguing here that heavy use of cannabis cannot be associated with a form of psychosis. The same can also be said regarding the heavy use of alcohol. In fact, heavy use of alcohol has been shown to cause organic psychosis and dementia.
But just as the risks associated with heavy alcohol use don’t argue for completely avoiding alcohol consumption in those without preexisting vulnerabilities, any risks that may correlate with heavy marijuana consumption don’t argue for completely avoiding marijuana in those who likewise lack preexisting vulnerabilities.
Perhaps Berenson could have considered a different title for his book, such as “Everything in Moderation.”