Frequent Cannabis Use Raises Psychosis Risk, Regardless of Genetics

A new study published in Psychological Medicine reveals that frequent use of cannabis, particularly high-potency varieties, raises the risk of developing psychosis regardless of an individual’s genetic predisposition for schizophrenia. The research was conducted by scientists at King’s College London’s Institute of Psychiatry, Psychology & Neuroscience (IoPPN) and the South London and Maudsley NHS Foundation Trust.

Exploring Cannabis Use and Genetic Risk for Psychosis

This pioneering study assessed both genetic risk for schizophrenia and cannabis use in relation to psychosis development. Researchers employed polygenic risk scores (PRSs)—which calculate genetic predisposition based on multiple small genetic variants—to analyze data from two large cohorts: the European Network of National Schizophrenia Networks Studying Gene-Environment Interactions (EU-GEI) and the UK Biobank. These datasets included 1592 participants from EU-GEI and 145,244 participants from UK Biobank.

Results demonstrated that frequent cannabis use was associated with a significantly increased risk of psychosis, particularly among daily users of high-potency cannabis (cannabis containing Delta-9 tetrahydrocannabinol levels of 10% or more). This association remained consistent even when accounting for the PRS for schizophrenia, highlighting that cannabis use raises psychosis risk through pathways independent of genetic predisposition.

The study further showed that the risk was highest among individuals with greater genetic susceptibility to schizophrenia who also use high-potency cannabis daily. Corresponding author Dr. Edoardo Spinazzola suggests these independent pathways “could potentially have an additive effect where those with increased genetic risk who use cannabis are highly likely to develop psychosis.”

These Findings Could Inform Preventative Strategies

The study's findings offer further insight into identifying those at risk of psychosis and creating targeted prevention strategies.

“Our study indicates that daily users of high potency cannabis are at increased risk of developing psychosis independently from their polygenic risk score for schizophrenia,”said lead author Professor Marta di Forti, “Nevertheless, the polygenic risk score for schizophrenia might, in the near future, become useful to identify those at risk for psychosis among less frequent users to enable early preventative measures to be put in place.”