A new study published in the journal Psychological Medicine estimates that teenagers who use cannabis are 11 times more likely to develop a psychotic disorder than their non-marijuana-smoking peers.
The paper is entitled “Age-Dependent Association of Cannabis Use with Risk of Psychotic Disorder”.
This finding suggests that the link between cannabis and psychotic disorders may be stronger than indicated in previous studies that relied heavily on older data, when it was less effective than it is today. For context, the average THC strength of cannabis in Canada has increased from approximately 1% in 1980 to 20% in 2018.
Researchers from the University of Toronto, the Center for Addiction and Mental Health (CAMH) and ICES linked recent data from a population-based survey of over 11,000 adolescents in Ontario, Canada to data on health service use, including hospitalizations, emergency room visits, and in an outpatient clinic.
“We found a very strong association between cannabis use and the risk of psychotic disorder in adolescence. But surprisingly, we found no evidence of a relationship in young adulthood,” says lead author Andre McDonald.
Of the teens who were hospitalized or visited the emergency room for a psychotic disorder, approximately 5 in 6 reported prior cannabis use. MacDonald’s observations indicate that “a large proportion of teenagers who use cannabis will not develop a psychotic disorder, but according to these data, most adolescents who are diagnosed with a psychotic disorder have a history of cannabis use.”
The researchers say they cannot completely rule out reverse causation, as adolescents with psychotic symptoms may have self-medicated with cannabis before receiving a clinical diagnosis.
They also cannot account for potentially important factors, such as genetics and trauma history. These limitations make it impossible to say definitively that teenage cannabis use causes psychotic disorders. The authors also note that their estimates are only approximate, suggesting that further studies are needed.
