The medical community has long debated whether or not regular cannabis use can increase one's chances of developing mental illness, but researchers have not yet been able to conclusively prove or disprove the claim. A number of studies have been able to identify that there is a correlation between cannabis use and mental illnesses like schizophrenia, but correlation does not imply causation.
In one recent study, researchers found that regular cannabis use can predict an increased risk of psychosis. The study’s authors wrote that “the most plausible hypothesis” explaining this connection is that “cannabis use precipitates schizophrenia in persons who are vulnerable because of a personal or family history of schizophrenia.”
But again, the study only identifies a correlation between the two factors, and not a causal link. “There are also other possible explanations of the association,” the researchers wrote. “Common factors may increase the risk of cannabis use and psychosis, without the two being directly related. Cannabis could also be used to self-medicate the symptoms of schizophrenia.”
A new study, published in the Nature Neuroscience journal, has found evidence supporting that the latter hypothesis may be the actual explanation for the connection between pot and schizophrenia. A team of scientists from the International Cannabis Consortium used genetic data from 23andMe and the UK Biobank to identify 35 genes associated with cannabis use. With data culled from over 180,000 people, this is one of the largest genetic studies on cannabis ever conducted.
The study found that cannabis use was most strongly associated with the gene known as CADM2. This gene “has already been associated with risky behavior, personality, and alcohol use,” Jacqueline Vink of Radboud University, lead author of the study, said in a statement. The study found genetic overlap between cannabis use and the use of alcohol and tobacco, as well as evidence that personality types connected with risky or extraverted behavior also overlapped with the population of cannabis users.
The study also confirmed a genetic overlap between cannabis use and schizophrenia, but the genetic nature of the study allowed researchers to investigate a causal link between the two factors, with a surprising result. “We also studied whether this association is causal,” Vink said. “Our study showed that people with a vulnerability to develop schizophrenia are at increased risk of using cannabis.”
This evidence supports the hypothesis that individuals suffering from schizophrenia are deliberately seeking out cannabis as a form of self-medication. The hypothesis is further supported by evidence reporting that cannabis may actually be able to effectively treat some symptoms of schizophrenia. A 2006 study found that schizophrenics who were self-medicating with pot had fewer negative symptoms than those who did not, and a 2012 study found that CBD treatments could be as effective as traditional antipsychotic drugs, but with fewer negative side-effects.
Although the study contradicts previous research suggesting that marijuana use increases the risk of schizophrenia, it still does not definitively end the debate. The researchers used a form of analysis called “Mendelian randomization” to provide strong evidence that schizophrenia increases the risk of pot use, but the technique does not allow scientists to conclusively disprove the previous research. As always, additional research must be undertaken to more fully understand the cannabis plant and its effects on the brain.