Study Shows Cannabis Does Not Cause Schizophrenia

Especially among prohibitionists, schizophrenia has long been raised as a potential risk of cannabis use. But new research refutes this implied causal relationship and clarifies the relationship between marijuana and mental illness, showing that schizophrenia may lead to cannabis use — not the other way around.

The research notes that the link between cannabis and schizophrenia is poorly understood and that figuring out the root cause of this link has proven a major challenge.

Schizophrenia is a lifelong mental disorder involving a breakdown in the relation between thought, emotion, and behavior. This leads to faulty perception, inappropriate actions and feelings,  a withdrawal from reality and personal relationships into fantasy and delusion and a sense of mental fragmentation. While schizophrenia is not curable, it can be treated.

Dr. Suzi Gage, one of the researchers at  Bristol’s School of Experimental Psychology told Science Daily that the data seems to suggest that schizophrenia can lead to cannabis use, not vice a versa:

“Our results use a novel method to attempt to untangle the association between cannabis and schizophrenia. While we find stronger evidence that schizophrenia risk predicts cannabis use, rather than the other way round, it doesn’t rule out a causal risk of cannabis use on schizophrenia,” Dr. Gage said.  “What will be interesting is digging deeper into the potential sub-populations of cannabis users who may be at greater risk, and getting a better handle on the impact of heavy cannabis use.”

Gage went on to note the researchers could only look at cannabis initiation, basically, whether anyone had ever tried cannabis ever or had not. She said more detailed information about use patterns would help the research.

“What would really help progress this research is to use genetic variants that predict heaviness of cannabis use, as it seems that heavy cannabis use is most strongly associated with risk of schizophrenia,” she said. “Once genetic variants are identified that predict heaviness of cannabis use we’ll be able to do this.”

Cannabis advocacy organizations have been battling back against the links between its use and mental health issues affecting certain users.

Among them, Paul Armentano, Deputy Director at the National Organization for the Reform of Marijuana Laws, who said this new data further solidifies the need for sane, humane drug policy.

“We argue that such health risk concerns call for regulation, not criminal prohibition,” he said. “So that cannabis’ use among more potentially vulnerable populations such as adolescents may be better discouraged through education and reduced access.”

Armentano has extensively covered the issue for NORML. In his 2007 report Cannabis, Mental Health, and Context: The Case For Regulation, he noted one issue with the current batch of research was where the data relied on participants using the pill Marinol. The all THC pill lacks the CBD, and its anxiolytic and antipsychotic effects.

“Separate studies have largely dismissed the theory that cannabis exposure may play a causal role in these illnesses, finding that rates of psychiatric disorders like schizophrenia have remained static even as cannabis exposure has significantly increased,”  Armentano said.

He closed on the most recent batch of research.

“A most recent literature review instead hypothesizes that that cannabis use does not cause the psychosis, but rather, that subjects susceptible to the disorder are more likely to engage in the early-onset use of the substance,” he said. “Evidence reviewed here suggests that cannabis does not in itself cause a psychosis disorder… rather, the evidence leads us to conclude that both early use and heavy use of cannabis are more likely in individuals with a vulnerability to psychosis.”

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