Contradicting widely held assumptions, newly published research indicates that a history of cannabis use does not significantly increase the likelihood of developing psychosis, even in people who already have a genetic or clinical predisposition to the condition.
A team of researchers drawn from Australia, Europe and the UK examined both current and past cannabis consumption across a cohort of 334 individuals deemed to be at clinical high risk of psychosis, alongside 67 healthy participants. All subjects were evaluated at the outset and monitored over a two-year follow-up period.
The transition to psychosis and whether psychotic symptoms persisted were measured using the Comprehensive Assessment of At-Risk Mental States criteria, while participants' overall functioning at follow-up was evaluated through the Global Assessment of Functioning disability scale.
By the end of the follow-up period, 16.2% of the clinical high-risk group had transitioned to psychosis. Among those who did not, 51.4% continued to experience symptoms associated with the condition, while 48.6% had entered remission.
Across every measure of cannabis use recorded at baseline, the researchers found no statistically significant association with transition to psychosis, ongoing symptom persistence, or functional outcomes.
The researchers said: "Our primary hypothesis was that cannabis use in clinically high-risk subjects would be associated with an increased rate of later transition to psychosis.
"However, there was no significant association with any measure of cannabis use."
While cannabis and other controlled substances tend to be used more frequently among people with psychotic illnesses, existing studies suggest that acute cannabis-induced psychosis is a relatively uncommon occurrence across the broader population.
Data published the previous year in the New Zealand Medical Journal similarly found that people with a history of cannabis use did not generally show more severe psychotic symptoms compared to those with no history of regular consumption.