You don’t have to be a pediatrician to know teens are facing more significant mental health challenges than ever before.
You also don’t have to be a pediatrician to know that cannabis (a.k.a. marijuana, pot, grass, or weed) is the most commonly used drug among teens in the United States.
A February 2026 Journal of the American Medical Association (JAMA) Health Forum study found that cannabis use in adolescents and young adults was associated with an increased risk of mental health disorders.
Study Design and Impactful Results
This study set out to determine if adolescent cannabis use was associated with an increased risk of developing psychiatric disorders by young adulthood.
In short, the answer was yes.
This large cohort study followed 463,396 adolescents through age 25 years in northern California and found that past-year cannabis use was associated with an increased risk of psychotic, bipolar, depressive and anxiety disorders.
The strongest associations with cannabis use were with bipolar disorder (2.0 times greater risk) and psychotic disorders (2.19 times greater risk) by age 26 years.
The onset of mental health symptoms followed the use of cannabis about 1.7 to 2.3 years earlier.
Of note, any amount of cannabis use in the past year was found to increase the risk of mental health disorders, not just daily or heavy use.
These statistics remained significant even after taking into account a history of mental health disorders and other substance use, and after excluding adolescents with prior mental health disease.
These findings also align with a meta-analysis showing 2.63 times greater odds of bipolar disorder associated with cannabis use.
What effect might THC (tetrahydrocannabinol) have on an adolescent brain?
THC is the primary psychoactive compound found in the cannabis plant and is responsible for the “high” associated with marijuana use.
The study notes that in northern California, the typical THC content of a cannabis flower exceeds 20%.
THC use during the teen years may disrupt the endocannabinoid system at a critical stage of brain development, especially the areas associated with motivation, emotional and affective processing.
Notably, the study found associations even when defining cannabis use as any past-year use (not just daily use), which is particularly concerning given that daily use and higher-strength products may have even stronger impact.
What is the take home message?
This JAMA Health Forum study published in February 2026 found that adolescent cannabis use is associated with an increased risk of psychiatric disorders in adolescents and young adults, even with only casual and occasional use.
These conclusions are so important for parents, teens, teachers, policy makers, and pediatricians to know, especially as marijuana is “mainstreamed” and legalized in more communities.
As an experienced pediatrician who cares for many adolescents with mental health challenges, these findings are not surprising.
But having these statistics at my fingertips is helpful when talking to my patients and their parents about the dangers of casual cannabis use and the negative impact that THC has on the developing teenage brain.