What happens when a teenager experiences
cannabis while his brain is still under construction? A major American study has just delivered precise figures, and they shake up the image of a simple “little smoke” without consequences.
Published in 2026 in the journal JAMA Health Forumthis research shows that young people aged 13 to 17 who report having used cannabis during the year have a risk doubled to later develop
psychotic disorders or a
bipolar disorder. Other disorders, such as depression and anxiety, are also increasing, which raises many questions.
A giant study on cannabis among adolescents
The team led by Kelly Young-Wolff analyzed the files of 463,396 adolescents followed within Kaiser Permanente Northern California. Between 2016 and 2023, these young people, initially aged 13 to 17, regularly answered a simple question during routine pediatric visits: “In the past year, have you used marijuana?“. At the start of the study, 5.7% reported use within the year. Doctors then followed the appearance of diagnoses of psychosis, bipolar disorder, depression or anxiety up to 25-26 years of age.
Result: among cannabis users, the risk of psychotic disorder was multiplied by 2.19 and that of bipolar disorder by 2.01. The risk of depression increased by about 34% and that of anxiety by about 24%. Diagnoses occurred on average 1.7 to 2.3 years after the first reported consumption.
“As cannabis becomes more potent and more aggressively marketed, this study indicates that adolescent cannabis use is associated with twice the risk of incident psychotic and bipolar disorders, two of the most serious mental health conditions” said Lynn Silver, program director Getting it Right from the Starta program of the Institute of Public Health, and co-author of the study.
Psychosis and bipolarity, rare but very serious disorders
THE psychotic disorders include, for example, schizophrenia, with hallucinations, delusions and break with reality. THE bipolar disorder alternates episodes of deep depression and phases of great excitement, sometimes dangerous for the person. Of the cohort, nearly 4,000 young people were diagnosed with psychosis and around 4,000 with a bipolar diagnosis.
“Evidence increasingly demonstrates the need for an urgent public health response — one that reduces product potency, prioritizes prevention, limits youth exposure and marketing, and treats adolescent cannabis use as a serious health problem, not a benign behavior“insists Dr. Lynn Silver
The authors point out that these diseases fortunately remain uncommon, but often chronic and disabling. In the files, adolescent users were also more often exposed to other substances and more frequently came from disadvantaged neighborhoods or from families covered by Medicaid (program covering the costs of people with limited resources), which raises questions about an accumulation of social and psychiatric vulnerabilities.
An adolescent brain more vulnerable to today’s THC
Researchers emphasize that the adolescent brain, still developing, is particularly sensitive to THC, the main psychoactive molecule of cannabis. The receptors of the endocannabinoid system, very present in the areas that manage emotions and motivation, can be disrupted by products that are now very concentrated: in California, the average content of flowers exceeds 20% THC and certain concentrates go up to 95%.
This is an observational study, which shows a strong association without proving direct causality on its own. However, the authors excluded already diagnosed young people, adjusted for alcohol and other drugs, and found these results even in those without a known psychiatric history. “This study adds to growing evidence that cannabis use during adolescence may have long-term adverse health effects. It is imperative that parents and their children have accurate, reliable, and evidence-based information regarding the risks of adolescent cannabis use” said Kelly Young-Wolff, lead author of the study and a senior research scientist at Kaiser Permanente.