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.”
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.
“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.”
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].