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Cannabis Connection: Does Pot Cause Schizophrenia?

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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.

Empirical Evidence

Researchers at the University of Exeter and University College London (UCL) argued in 2016 that cannabis-induced psychosis affects one percent of users, while The British Journal of Psychiatry in 2004 said ending all cannabis use would decrease schizophrenia by eight percent worldwide. These findings contrast the 2009 Addiction study, but the empirical evidence heavily favors the latter.

Gallup asked about cannabis for the first time in a 1969 poll, and four percent of the participants said they tried it. In the 2015 poll, the figure jumped to 44 percent, marking an elevenfold increase, with one in eight U.S. adults regularly smoking cannabis as of 2016. These percentages mark a significant increase in usage, so naturally the rate of incidence for schizophrenia went up proportionally, right? Wrong. The British Journal of Psychiatry would make you think the rate increased by up to eight percent, but it actually remained steady at around one percent, with Schizophrenia Bulletin suggesting in 1995 that rates have been on the decline. Moreover, this decline occurred at a time when increased awareness and decreased stigma arguably made it easier to recognize the symptoms and diagnose more cases.

In 2015, the Nature journal published a study that said “the assertion that cannabis use can cause schizophrenia is not borne out by the evidence.” Among the many arguments, the study pointed to the empirical evidence both in the U.S. and on a global scale. The author, who also whupped ass on the 1987 Lancet study here, is not the only researcher to emphasize the empirical evidence. For example, a 2003 Australia-based study in Drug and Alcohol Dependence concluded, “There was a steep rise in the prevalence of cannabis use in Australia over the past 30 years and a corresponding decrease in the age of initiation of cannabis use. There was no evidence of a significant increase in the incidence of schizophrenia over the past 30 years.”

What Does the U.S. Government Say

The FDA is hardly a friend of the cannabis community, and its 2015 “Recommendation to Maintain Marijuana in Schedule I of the Controlled Substances Act” reiterated its indefensible stance that coke, meth and opioid painkillers have more medical value and less risk than cannabis. Nevertheless, the 56-page report tackled the cannabis-schizophrenia link directly and concluded the following:

“Extensive research has been conducted to investigate whether exposure to marijuana is associated with the development of schizophrenia or other psychoses. Although many studies are small and inferential, other studies in the literature use hundreds to thousands of subjects. At present, the available data do not suggest a causative link between marijuana use and the development of psychosis. Numerous large, longitudinal studies show that subjects who used marijuana do not have a greater incidence of psychotic diagnoses compared to those who do not use marijuana…. Although evidence shows that marijuana use may precede the presentation of symptoms in individuals later diagnosed with psychosis, most reports conclude that prodromal symptoms of schizophrenia appear prior to marijuana use.”

In 2015, the typically anti-cannabis National Institute on Drug Abuse (NIDA) introduced the “Is Marijuana Medicine?” DrugFacts page, and it changed the title in 2017 to “Marijuana as Medicine” with a list of disorders it might help treat. NIDA then seemed to throw shade at the FDA saying it was the agency currently withholding the federal recognition that cannabis has medical benefits. In other words, the FDA did not easily dismiss the cannabis-schizophrenia claim, and it took a Freedom of Information Act (FOIA) request for the public to know it even had.

The Verdict

At present, the evidence suggests the link is merely a correlation with shared vulnerabilities contributing to the disorder and motivating cannabis use, and if there is a causal link, it’s weak and rare and possibly associated only with a specific genetic abnormality. Additional studies should provide more clarity either way, but there will always be more questions than answers as long as the federal government maintains what could be described as Draconian restrictions on cannabis research.

And speaking of more questions, try this one on for size: Can cannabis help treat schizophrenia?

Researchers gave the cannabis compound cannabidiol (CBD) to rats with mental health disorders, and Neuropsychopharmacology published the findings in June 2017. It said CBD appeared to improve schizophrenia-specific cognitive impairment without any of the nasty side effects associated with prescription medication. Per the study, “These novel findings present interesting implications for potential use of CBD in treating the cognitive deficits and social withdrawal of schizophrenia.”

In other words, future studies might confirm that cannabis does play a role in schizophrenia, but that role might be as a treatment for certain schizophrenia symptoms.


David Jenison is a Los Angeles native and the editor-in-chief of PROHBTD. He has covered entertainment, restaurants and travel for more than 20 years.

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