Research published Friday in JAMA Health Forum indicates that teenagers who use marijuana face a heightened risk of developing psychotic disorders, bipolar disorder, anxiety, and depression as they age. The study, which tracked 460,000 adolescents in Northern California until age 25, excluded those who exhibited prior mental health symptoms to isolate the effects of cannabis.

“This cohort study found that adolescent cannabis use was associated with increased risk of incident psychiatric disorders, particularly psychotic and bipolar disorders,” the authors wrote, noting that the findings could inform educational and clinical interventions as well as policies aimed at delaying or preventing teen marijuana use in the context of expanding legalization.

Columbia University psychiatrist Dr. Ryan Sultan described the findings as “very, very, very worrying,” highlighting the potential long-term impact on mental health. Teens who reported cannabis use were found to double their risk of developing psychotic disorders, including schizophrenia, and bipolar disorder. Although only about 4,000 of the teens were diagnosed with these disorders, both are considered among the most serious and disabling mental illnesses, with high societal costs.

Experts emphasize the increasing potency of today’s cannabis products, which contain two to three times more THC than in previous decades. Adolescent use is particularly concerning because the teenage brain is still developing critical neural connections, making cognitive functions related to learning and academic performance especially vulnerable.

Columbia University’s Irving Medical Center reported in December that roughly one in five high schoolers currently use cannabis. Meanwhile, experts in 2025 noted that while more Americans were developing cannabis dependence, fewer were seeking treatment, signaling a growing public health concern.