A common rebuttal to promotion of cannabis as part of a healthy lifestyle is the assertion that cannabis is linked to mental health disorders such as schizophrenia, a connection that has come up again and again in research. Cannabis enthusiasts have always been skeptical about the causality involved - about whether cannabis actually causes schizophrenia. For their part, researchers have failed to firmly establish that causality. Now, according to Rolling Stone, a new study offers an explanation that validates what many cannabis advocates have long suspected.

In the largest study yet of its kind, researchers with the International Cannabis Consortium project analyzed the genetic data of more than 180,000 individuals obtained from other studies or 23andMe’s database. They have called the evidence “weak” for the potential of cannabis to cause schizophrenia, instead finding solid evidence that the early symptoms experienced by those at risk for schizophrenia causes them to attempt self-medication with cannabis.  According to the study, these symptoms “make them more likely to start using cannabis to cope or self-medicate”.

"Our study showed that people with a vulnerability to develop schizophrenia are at increased risk of using cannabis," explains Jacqueline Vink, the study’s lead author and a professor at Radboud University in the Netherlands.  According to the researchers, this confirms a “significant genetic correlation”.  A previous study in 2014 came to the same conclusion, finding that the genes that put people at risk for schizophrenia are also associated with cannabis use. Thus, the results of these studies controvert the traditional assumptions regarding causality.

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The new study is much larger than the 2014 study and takes a more comprehensive view of the genetics. The report was published in the journal Nature Neuroscience, and includes work from 80 researchers around the world. The report also links cannabis use to a range of other life attributes, including higher education levels and higher income, which could be explained by greater access to cannabis, as well as higher levels of “openness to experience” and risk-taking behavior.

The study has its limitations. It did nothing to differentiate between heavy and occasional users, or between medical and recreational use. People examined in the study were simply grouped into categories of users and non-users – regardless whether they had tried it once or currently smoked daily and whether they had cannabis recommended by a doctor or simply passed a joint around at a party every weekend. All of these factors were not accounted for in the study and could have a real bearing on the relationship between cannabis and mental health.

However, the results do highlight some of the pitfalls that have plagued past studies in their attempt to objectively analyze the evidence. As Amelia McDonell-Parry writes in Rolling Stone:

“A significant factor that many of these studies struggle to consider are the benefits of marijuana use in coping with those symptoms. One reason could be that evidence of these benefits may be anecdotal, but not necessarily measurable in the ways traditional science considers valid or quantifiable.”

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This notion of anecdotal, but difficult to quantify, benefits is likely to ring true for cannabis users. Some of the benefits of cannabis may be subjective – but that doesn’t make them any less relevant.

Also, since cannabis use can, in theory, be controlled by personal choice and legal limitations, researchers in the past may have tended to view cannabis as the cause and the more elusive mental illness as the result.

People with schizophrenia seem to be more likely to use cannabis, but the idea that cannabis is actually causing or worsening the schizophrenia may turn out to be an assumption from the prohibition era, when cannabis was generally considered guilty until proven innocent. 

On a related note, another study published in the journal JAMA Psychiatry this week suggests that CBD may suppress some of the symptoms of psychosis. Patients who took a single 600 mg dose of CBD were found, in the hours afterward, to have lower levels of abnormal activity in parts of the brain linked to psychosis.

Together these studies suggest that scientists are only just beginning to piece together the puzzle of the relationship between cannabis and mental health disorders. The timing is no coincidence. As society begins to view cannabis differently and to loosen legal constraints, scientists are more likely to be able to do research that is truly objective and free of assumptions. Only then will we understand the real potential of cannabis. And in many cases, the new research is supporting what cannabis users have already been saying for decades.