When alcohol prohibition ended in 1933, the anti-booze bureaucracy turned its attention to cannabis, and Harry Anslinger—the former second in command at the Prohibition Bureau—led the charge with claims that cannabis caused people to murder, rape and steal. Anslinger achieved his goal of cannabis prohibition 80 years ago this summer, and the judge who condemned the first offender declared, “Marijuana [is] the worst of all narcotics, far worse than the use of morphine or cocaine. Under its influence men become beasts. Marijuana destroys life itself.”
Quite the overstatement, no?
Well, a lot of people thought so, and by the 1940s, the public largely dismissed the idea that smoking reefer can make you mad like Jack Nicholson in The Shining. In response, the prohibition effort invented new claims (e.g., the gateway drug theory) and scare tactics (e.g., “Marijuana caused acne, blindness, and sterility”), but the most effective propaganda involved a new spin on an old classic. The bureaucrats repackaged “men become beasts” as schizophrenia and psychosis.
Many claims have been made about cannabis risks, but the schizophrenia link is likely the most hotly debated. The divide typically falls into two camps: Some argue that cannabis is a direct contributing cause, while others say shared vulnerabilities explain any potential overlap.
Cannabis Causes Crazy
Schizophrenia likely involves an imbalance of neural chemical reactions and/or faulty neural connections typically caused by a combination of genetic and environmental factors. A schizophrenic is actually not crazy, but the symptoms can be strong, and they can include hallucinations, delusions, confusion and aggression. Cannabis, many argue, is one of the environmental factors that can contribute to schizophrenia, and this theory increased in prominence during the drug war-driven 1980s.
In 1987, The Lancet published a longitudinal study involving nearly 46,000 Swedes, and it found that heavy users tend to have a higher risk of schizophrenia. This particular study added credibility to the longtime assertion, and additional research quickly ramped up. Among many examples, Archives of General Psychiatry in 2011 found that symptoms of schizophrenia typically manifest 2.7 years earlier for cannabis consumers, while a 2014 review in Frontiers in Psychiatry suggested that cannabis “may be a component cause in the emergence of psychosis.” The latter study also said it might produce “a full range of transient psychotomimetic symptoms, cognitive deficits, and psychophysiological abnormalities that bear a striking resemblance to symptoms of schizophrenia.”
More recently, researchers tested cannabis on several young mice, including a group genetically susceptible to schizophrenia, and published the findings in 2017 in Human Molecular Genetics. The study said cannabis-using, genetically susceptible mice had a higher risk of brain defects associated with the onset of the disorder. The lead researcher concluded, “Young people with a genetic susceptibility to schizophrenia—those who have psychiatric disorders in their families—should bear in mind that they’re playing with fire if they smoke pot during adolescence.”
Recent studies also suggest abnormalities in a particular gene (AKT1) make cannabis users more vulnerable, and potent strains and adolescent use contribute to the onset of psychosis and schizophrenia.
Cannabis Doesn’t Cause Crazy
According to a study published in Schizophrenia Research in 2013, psychosis patients who smoke cannabis are way smarter. To quote directly, “Patients who had ever smoked cannabis had significantly higher current and premorbid IQ compared to patients who had never used cannabis. This difference was not found among controls.”
This data suggests that cannabis increases your IQ!
Actually, it doesn’t. Mental health disorders and significantly higher IQs might be more common among cannabis consumers, but the evidence shows a correlation, not the cause. Smart people might simply be more inclined to ignore the drug-war propaganda and/or more easily recognize that cannabis (at least temporarily) reduced or masked symptoms. Regarding the latter, studies suggest people with undiagnosed mental health disorders often turn to cannabis, alcohol and non-prescribed pharmaceuticals to self-medicate the symptoms, in which case cannabis use is in reaction to, not the cause of, the disorder.
In other words, cannabis might not increase your risk of developing schizophrenia, but schizophrenia might increase your risk of self-medicating with cannabis.
Most studies cited by the cannabis-causes-crazy crowd simply demonstrate a correlation, and the basic principle that correlation does not imply causation is often ignored when it comes to cannabis. To quote conservative icon and National Review founder William F. Buckley, “The thunderers who tell us to stay the course [on prohibition] can always find one man or woman who, having taken marijuana, moved on to severe mental disorder. But that argument… is on the order of saying that every rapist began by masturbating.”
Many researchers also put the cannabis-schizophrenia correlation to the test and found little or no causal evidence, and studies cited by causation proponents are often less definitive than they suggest. For example, consider this passage from the aforementioned study about symptoms emerging 2.7 years earlier: “Not all researchers agree that the association between cannabis use and earlier age at onset is causal…. [It] could be explained by demographic variables, including lower socioeconomic status and the proportion of male cannabis users…. [Likewise,] the apparent association… might simply be owing to older patients with first-episode psychosis being less likely to use cannabis.”
Other research more adamantly refutes causation.
A 2005 study in Biological Psychiatry found that “cannabis use had no such adverse influence,” while Current Psychiatry Reports argued in 2016 that cannabis, tobacco use and poor school performance might be warning signs that a teen has a disorder, but “cannabis does not in itself cause a psychosis disorder.” A 2015 study in Psychology of Addictive Behaviors looked at four different trajectory groups (from non-user to chronic) and found no significant difference in terms of physical and mental health (and the insignificant differences typically favored the chronic user). The lead researcher said in a press release, “There were no differences in any of the mental or physical health outcomes that we measured regardless of the amount or frequency of marijuana used during adolescence.”
The Addiction journal in 2017 said cannabis might exacerbate symptoms in a person who already has schizophrenia, but it highlights the need to define the level of risk. In this case, the researchers argued that “the increased risk is weak and the vulnerabilities relatively rare” and that the best way to address the problem is through legalization. “Regulation could help reduce the risks to health that cannabis use poses,” said the study, “as a regulated cannabis market would introduce some quality control.”
As for the level of risk, a 2009 Addiction study asked how many people would have to give up cannabis to prevent one case of schizophrenia per year, if such a direct link does exist. Among heavy users, 2,800 males between the age of 20 and 24 (the high-risk group) or nearly 11,000 females age 35 to 39 (the low-risk group) would need to stop to prevent one case. For casual users, those numbers skyrocket to 14,000 for men or 55,000 for women, which compares favorably to the Food and Drug Administration (FDA) warning that one in 530 people who take Klonopin experience suicidal thoughts and intentions.