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Schizophrenia risk may predict cannabis initiation

Recent findings indicated a causal effect of cannabis initiation on schizophrenia risk, suggesting schizophrenia risk may predict cannabis initiation and not vice versa.

“The evidence suggested that schizophrenia risk predicts the likelihood of trying cannabis,” Suzanne Gage, BSs, MSc, of University of Bristol, United Kingdom, said in a press release. “However, the relationship could operate in both directions. Our results don’t really allow us to accurately predict the size of the effect — they're more about providing evidence that the relationship is actually causal, rather than the result of confounding or common risk factors.”

To determine causality in associations between cannabis use and schizophrenia, researchers analyzed genome-wide data from the International Cannabis Consortium and the Psychiatric Genomics Consortium for 36,989 individuals with schizophrenia and 113,075 controls.

There was a small association between cannabis initiation and schizophrenia case status (OR = 1.04; 95% CI, 1.01-1.07; P = .019).

There was strong evidence of an association between schizophrenia and lifetime cannabis initiation (OR = 1.1; 95% CI, 1.05-1.14).

Fewer years of education and height were not strongly associated with cannabis initiation.

“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 around, it doesn’t rule out a causal risk of cannabis use on schizophrenia,” Gage said in the release. “What will be interesting is digging deeper in to the potential subpopulations of cannabis users who may be at greater risk, and getting a better handle on the impact of heavy cannabis use.” – by Amanda Oldt

Disclosure: The researchers report no relevant financial disclosures.