Washington University in St. Louis researchers have found that adolescents who use cannabis report more psychosis spectrum symptoms and greater distress from these symptoms, suggesting that shared vulnerability and self-medication contribute to the association between cannabis use and psychosis risk.

Cannabis use among adolescents has been associated with a higher risk of psychosis, with users being two to four times more likely to develop psychosis than non-users. Early initiation during adolescence is linked to earlier onset of psychotic disorders, more severe symptoms, and a greater likelihood of symptom relapse.

Cannabis is the most frequently used illicit substance among adolescents, with usage increasing from 11% to 22% over the past two decades, according to a source cited in the study. Perceived risk of harm associated with cannabis use has decreased among adolescents, dropping from 36.3% to 25%, considering weekly use as problematic.

Debate continues regarding the nature of the association between adolescent cannabis use and psychosis risk, with theories including the contributing risk hypothesis, the shared vulnerability hypothesis, and the self-medication hypothesis.

In the contributing risk hypothesis, cannabis use causes the emergence and progression of psychosis through disruption of the neurodevelopmental processes during adolescence.

According to the shared vulnerability hypothesis, genetic, gestational, or environmental factors predispose individuals to both cannabis use and psychosis. In this scenario, the likelihood of engaging in cannabis use shares the same origin as the risk of psychosis spectrum symptoms.

The self-medication hypothesis suggests that individuals may turn to cannabis use as a means to alleviate distressing symptoms associated with the psychosis spectrum.

Previous research has provided evidence supporting each of these models, but there is a lack of prospective longitudinal studies focusing on early adolescence.

In a study, "Psychosis Spectrum Symptoms Before and After Adolescent Cannabis Use Initiation," published online in JAMA Psychiatry, the researchers analyzed psychosis spectrum symptom trajectories before and after cannabis initiation in 11,868 adolescents aged 9 to 10 years at baseline using data from five waves over four years from the Adolescent Brain Cognitive Development (ABCD) Study.

Cannabis initiation did not consistently lead to an increase in psychosis symptoms, providing no significant support for the contributing risk hypothesis.

Adolescents who used cannabis at any point during the study period reported a greater number of psychosis spectrum symptoms and more distress compared to those who never used cannabis, supporting the shared vulnerability hypothesis.

An increase in the number of psychosis spectrum symptoms and associated distress leading up to cannabis initiation was observed before cannabis use started, aligning well with the self-medication hypothesis.

Based on the findings, the current research supports the shared vulnerability and self-medication explanations for the associations between cannabis use and psychosis risk.

More information: K. Juston Osborne et al, Psychosis Spectrum Symptoms Before and After Adolescent Cannabis Use Initiation, JAMA Psychiatry (2024). DOI: 10.1001/jamapsychiatry.2024.3525

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