A study of data from nearly half a million young people has found that adolescent cannabis use is associated with an increased risk of being diagnosed with multiple psychiatric disorders in early adulthood.
The study, published in the journal Jama Health Forum, utilised data from 463,598 adolescents aged 13 to 17 via the Teen Well-Check Questionnaire (TWCQ), a survey used extensively across America, as well as electronic health records.
Researchers found that past-year cannabis use was associated with more than double the risk of being diagnosed with psychotic disorders (adjusted hazard ratio 2.19) and bipolar disorder (adjusted hazard ratio 2.01) in early adulthood. The study also identified increased risks for depressive disorders (adjusted hazard ratio 1.34) and anxiety disorders (adjusted hazard ratio 1.24).
To be included in the study, participants must have been enrolled with Kaiser Permanente Northern California (KPNC), a nonprofit healthcare provider established in the 1960s by Harry Kaiser, a construction tycoon. Participants were also required to have responded to the question about cannabis use in the TWCQ.
Researchers followed cohort members until they reached the age of 25, or until data collection ceased in 2023. The study ran from 2016 until 2025, with data analysis taking place in 2024 and 2025.
The study utilised Cox proportional hazards regression models to determine the strength of the associations between adolescent cannabis use and incident psychiatric diagnoses to “estimate the association between time-varying cannabis use and incidence of each psychiatric disorder”. The strongest associations were found for psychotic and bipolar disorders.
Adjustments were made for variables, as the study author explains, “All models were adjusted for sex, race and ethnicity, NDI, insurance type, and alcohol and other substance use. Cannabis, alcohol, and other substance use were modelled as time-varying covariates and were updated at each well-child visit. To account for shared genetic and environmental factors, we clustered adolescents within families using robust SEs.”
In their conclusion, the researchers called for more prevention efforts and policy strategies to protect young people from the potential harms cannabis can cause.
“To our knowledge, this is among the largest longitudinal studies to examine cannabis use in adolescence and its association with the incidence of clinician-diagnosed psychiatric disorders into young adulthood,” the study authors wrote.
“Using population-level electronic health record-based clinical data, we found that adolescent cannabis use was associated with an increased risk of multiple psychiatric disorders by early adulthood. Associations were stronger for psychotic and bipolar disorders.
“These results are consistent with cannabis being a risk factor for or exacerbating the risk of psychiatric disorders rather than only resulting from pre-existing psychiatric conditions. These findings reinforce the need for early prevention efforts, stronger public health messaging, and policy strategies that limit youth exposure in the context of expanding cannabis legalisation.”
The researchers acknowledged that reverse causation cannot be ruled out entirely, as some individuals may use cannabis to self-medicate early symptoms of psychiatric disorders before formal diagnosis.
Kelly Young-Wolff, lead author of the study and senior research scientist at the Kaiser Permanente Division of Research, said: “Even after accounting for prior mental health conditions and other substance use, adolescents who reported cannabis use had a substantially higher risk of developing psychiatric disorders – particularly psychotic and bipolar disorders. This study adds to the growing body of evidence that cannabis use during adolescence could have potentially detrimental, long-term health effects.”
The study also called for further research with more nuanced measurement of cannabis use, including frequency, mode of use, and product strength, alongside regular screening and assessment for psychiatric disorder symptoms and diagnosis.
