Cannabis exposure and its link to psychosis has long been a topic of scientific inquiry, although there are still significant gaps in understanding why and how prevalent these episodes are.
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A new comprehensive analysis, aggregating data from over 201,000 participants, seeks to clarify this relationship.
While individual studies have previously reported a wide range of psychosis incidences among cannabis users, from as low as 1% to as high as 70%, this new analysis narrows it down. The study suggests that approximately one in 200 users (0.5%) may experience a psychotic episode, characterized by symptoms such as hallucinations, delusions and paranoia.
Published June 3 in Nature Mental Health, the new study notes that "no research has yet synthesized and compared the findings obtained from different study designs and populations."
Historically, studies have suggested that genetic factors, particularly genes associated with schizophrenia, might explain why some cannabis users develop psychosis while others do not.
This new analysis finds that young adults, women and those with pre-existing mental health conditions such as bipolar disorder are more at risk than others.
The research team, led by statistical geneticist Tabea Schoeler from the University of Lausanne in Switzerland and her colleagues scrutinized 162 high-quality studies for their analysis.
Most of the 201,283 participants had been part of observational studies assessing the experiences of recreational cannabis users and looking for links to demographic, social and genetic factors.
The rates of cannabis-associated psychosis varied significantly across study types: observational and experimental research reported high rates of 19% and 21%, respectively, while medicinal cannabis studies reported a lower rate of around 2%.
“The availability of these three distinct lines of evidence provides a unique research opportunity as their findings can be synthesized, be inspected for convergence, and ultimately, contribute to more evidence-based harm-reduction initiatives,” Schoeler and her colleagues wrote, adding that “not every individual exposed to cannabis is equally at risk.”
No Genetic Link
Interestingly, the analysis found no significant association with the genes COMT and AKT1, the genes that have previously been implicated in the interaction between cannabis-related psychosis. The researchers said this suggests the need to reconsider these genetic links.
The study found that early and frequent cannabis exposure did not increase the risk of psychotic episodes, though warned that daily use could still elevate the long-term risk of developing psychosis.
"Some individuals appear to be particularly sensitive to the adverse acute effects of cannabis, notably young individuals with pre-existing mental health problems and individuals exposed to high levels of THC," concluded the authors. "Future studies should therefore monitor more closely adverse cannabis-related outcomes in vulnerable individuals as these individuals may benefit most from harm-reduction efforts."
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