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Schizophrenia Risk May Predict Cannabis Use

January 04, 2017

While some evidence suggests cannabis use raises schizophrenia risk, a new study found stronger evidence that people at greater risk of developing schizophrenia are more likely to try cannabis.

Researchers published their findings, which support the idea that such people may use cannabis in an attempt to self-medicate, online in Psychological Medicine.

“The evidence suggested that schizophrenia risk predicts the likelihood of trying cannabis,” said researcher Suzi Gage, PhD, research associate at the University of Bristol in England. “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.”

Cannabis Use Patterns Correlate With Psychosis Relapse Risk

The study applied Mendelian randomization techniques to data from genome-wide association studies. A type of instrumental variable analysis, Mendelian randomization uses genetic variants to predict either risk of cannabis use or risk of developing schizophrenia. The techniques aimed to account for additional variants that may affect the cannabis-schizophrenia association.

The study found some evidence that cannabis use may contribute to raising schizophrenia risk. However, the evidence was stronger that increased schizophrenia risk raises the likelihood of cannabis use.

Cannabis Use Tied to Poorer Outcomes in Patients With First Psychosis

“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 in to 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.”

—Jolynn Tumolo


Gage SH, Jones HJ, Burgess S, et al. Assessing causality in associations between cannabis use and schizophrenia risk: a two-sample Mendelian randomization study. Psychological Medicine. 2016 December 8;[Epub ahead of print].

Further evidence found for causal links between cannabis and schizophrenia [press release]. Bristol, England: University of Bristol; December 19, 2016.

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