Adolescent cannabis use linked to higher risk of psychotic disorders, study finds

By Priyanjana Pramanik, MSc.Reviewed by Benedette Cuffari, M.Sc.May 26 2024

In a recent study published in the journal Psychological Medicine, researchers investigate the link between psychotic disorders and youth cannabis use. To this end, cannabis use was found to increase the risk of psychotic disorders during adolescence significantly but not during young adulthood, with this risk notably higher in the context of more potent cannabis products currently on the market.

Study: Age-dependent association of cannabis use with risk of psychotic disorder. Image Credit: Kovalevich28 / Shutterstock.com

Background

Previous research indicates a possible link between psychotic disorders and youth cannabis use, with studies identifying an increased likelihood of psychotic disorders among cannabis users. However, these studies often rely on older data when cannabis products were less potent. Many of these studies are also associated with important limitations, including small sample sizes and less clinically relevant outcomes.

About the study

The current study used recent population-based data to estimate the strength of the association between cannabis use during youth and the risk of developing a clinically diagnosed psychotic disorder. The researchers were also interested in providing updated evidence on the relationship between cannabis use and psychotic disorders, considering recent increases in cannabis potency.

The current analysis used data from the 2009 to 2012 cycles of the Canadian Community Health Survey (CCHS) linked to administrative health data in Ontario. All study participants were Ontario residents between 12 and 24 years of age at the time of the survey. Individuals with a history of prior psychotic disorders or incomplete health records were excluded from the analysis, leading to a final sample size of 11,363.

Data on cannabis use, sociodemographic factors, and other substance use were collected through in-person and telephone interviews. The primary outcome was time to first health service contact for a psychotic disorder, which was identified using validated diagnostic codes. All study participants were followed for up to nine years, with the maximum follow-up period ending in 2018.

The current study employed a multivariable Cox proportional hazards model to estimate the association between cannabis use in the preceding year and the risk of developing a psychotic disorder. All observations were adjusted for confounding factors such as age, sex, race, income, and other substance use.

Sensitivity analyses were conducted to test the robustness of the findings, including adjustments for different confounding factors and excluding specific subgroups.

Study findings

About 23.4% of the 11,363 respondents reported using cannabis in the past year. During the follow-up period, 1.2% of respondents used healthcare services for psychotic disorders.

The multivariable extended Cox model showed a significant association between cannabis use in the previous year and psychotic disorders among adolescents between 12 and 19 years of age, with an adjusted hazard ratio (aHR) of 11.21. This association was not observed among young adults between 20 and 33, with an aHR of 1.29.

Sensitivity analyses reinforced the robustness of these findings, with an aHR of 26.68 for hospitalizations or medical visits related to psychotic disorders among adolescents who used cannabis.

A dose-response relationship was observed, with weekly or more frequent cannabis use among adolescents associated with a higher risk and aHR of 10.70. Gender-specific analysis indicated that this association was significant for adolescent males, with an aHR of 9.98.

Prior healthcare service use for psychotic disorders was significantly associated with reporting cannabis use in the preceding year, with an aHR of 1.41, thus suggesting possible reverse causation.

Conclusions

Using cannabis between ages 12 and 19 was associated with an eleven-fold increased risk of developing a psychotic disorder. However, no significant association was observed between 20 and 33 young adults. Taken together, these findings indicate that adolescents may be more sensitive to the impact of cannabis on psychotic disorders.

Some strengths of the current study include using high-quality and representative data from the CCHS and linked healthcare service data, a validated health service use outcome, and recent data reflecting contemporary cannabis potency. However, notable limitations include the potential of unmeasured confounding factors such as genetic predisposition, family history, or trauma, as well as the reliance on self-reported cannabis use and a single baseline measurement.

The findings are also limited by the inability to establish temporality and control for time-varying confounding factors. Despite these limitations, the current study suggests that the rising potency of cannabis could explain the observed stronger association compared to previous research.

These implications are significant for public health and policy, particularly regarding adolescent cannabis use prevention. Thus, future research should include longitudinal studies with better cannabis use measurement, comprehensive confounder control, and consideration of genetic and environmental moderators to strengthen causal inference. Furthermore, there remains a need for evidence-based strategies to mitigate the risks of cannabis use during adolescence as more regions liberalize cannabis laws.