--- title: "Adolescent Cannabis Use and Mental Health: What the Largest Long-Term Studies Now Show" slug: adolescent-cannabis-mental-health-psychosis-bipolar-2026 category: health category_label: "Health" author: "BrainWavePost Staff" date: 2026-06-28 tags: ["adolescent health", "mental health", "cannabis", "psychosis", "bipolar disorder", "schizophrenia", "neurodevelopment", "JAMA", "NIDA", "CDC"] read_time_minutes: 9 canonical_url: https://brainwavepost.com/article/adolescent-cannabis-mental-health-psychosis-bipolar-2026 source: BrainWavePost --- # Adolescent Cannabis Use and Mental Health: What the Largest Long-Term Studies Now Show *Health · 2026-06-28 · BrainWavePost Staff · 9 min read* > New long-term research published in JAMA Health Forum — together with nationwide registry studies in JAMA Psychiatry and Psychological Medicine — adds rigorous evidence linking early cannabis use to increased risk of psychotic and bipolar disorders in young adulthood. > **Educational summary — not medical advice** _(note)_ > > This article summarises peer-reviewed research and public-health guidance. It is for general information only and is not a substitute for professional medical, psychological, or psychiatric advice. Parents, teens, and clinicians who have specific concerns should consult a qualified healthcare provider. Sources cited inline are from JAMA Network, Cambridge University Press, the U.S. National Institute on Drug Abuse (NIDA), the U.S. Centers for Disease Control and Prevention (CDC), and the American Academy of Pediatrics (AAP). [1][2][3][4][5][6] A growing body of large-scale, long-term research is sharpening what scientists and clinicians can say about the relationship between cannabis use in adolescence and serious mental-health outcomes in young adulthood. The most recent addition is a 2026 cohort study of more than 460,000 U.S. adolescents published in JAMA Health Forum, which builds on landmark Danish nationwide registry studies released in 2023. [1][2][3] ## What the new 2026 U.S. study found Published on February 20, 2026 in JAMA Health Forum, the study by Young-Wolff and colleagues followed 463,396 adolescents aged 13–17 in the Kaiser Permanente Northern California integrated health system from 2016 through 2023, with outcomes tracked through age 25. [1] After adjusting for sex, race and ethnicity, insurance type, neighbourhood deprivation, and concurrent alcohol or other substance use, adolescents who reported past-year cannabis use had higher rates of new psychiatric diagnoses by young adulthood: adjusted hazard ratio (AHR) 2.19 for psychotic disorders, AHR 2.01 for bipolar disorder, AHR 1.34 for depressive disorders, and AHR 1.24 for anxiety disorders. [1] In plain terms, teens who used cannabis in the prior year were roughly twice as likely to develop a psychotic or bipolar disorder compared with non-using peers in the same health system. [1] - **463,396** — U.S. adolescents followed in the 2026 JAMA Health Forum cohort [1] - **AHR 2.19** — Adjusted hazard ratio for psychotic disorders with past-year teen cannabis use [1] - **AHR 2.01** — Adjusted hazard ratio for bipolar disorder with past-year teen cannabis use [1] ## Nationwide Danish registries: depression, bipolar, and psychosis A 2023 JAMA Psychiatry study by Jefsen and colleagues analysed Danish nationwide health registers covering 6,651,765 individuals followed for nearly 120 million person-years between 1995 and 2021. [2] Cannabis use disorder was associated with an increased risk of unipolar depression (hazard ratio [HR] 1.84), psychotic unipolar depression (HR 1.97), bipolar disorder in men (HR 2.96) and women (HR 2.54), and psychotic bipolar disorder (HR 4.05). [2] The study adjusted for alcohol use disorder, parental psychiatric history, and other key confounders. [2] A separate 2023 study in Psychological Medicine — co-authored by then-NIDA Director Nora D. Volkow — followed 6.9 million Danes over five decades and found the association between cannabis use disorder and schizophrenia was strongest in young males. [3] Among 16–20-year-old males, the adjusted incidence rate ratio reached 3.84. [3] The NIDA press release on the paper notes the authors estimated that as many as 30% of schizophrenia cases among men aged 21–30 might have been averted if cannabis use disorder had been prevented. [4] > Increases in the legalization of cannabis over the past few decades have made it one of the most frequently used psychoactive substances in the world, while also decreasing the public's perception of its harm. This study adds to growing evidence that cannabis use is not harmless, and that taking steps to prevent or treat cannabis use disorder, especially in young men, could be a way to prevent or reduce cases of schizophrenia. > > — Nora D. Volkow, M.D., Director, National Institute on Drug Abuse (NIDA), 2023 [4] ## Why adolescence matters: a critical window for the brain The CDC notes that cannabis use can have lasting effects on the developing brain when use begins in adolescence, particularly with regular or heavy use. [5] CDC surveillance also shows that in 2022, 30.7% of U.S. 12th-graders reported past-year cannabis use, and 6.3% reported daily use in the prior 30 days. [5] The American Academy of Pediatrics, through its parent-facing HealthyChildren.org platform, reports that while roughly 9% of people who use cannabis develop a cannabis use disorder, the rate climbs to about 17% for those who start in their teens. [6] The AAP describes cannabis as a possible trigger for the psychosis that can be an early sign of schizophrenia or bipolar disorder, and its policy position is that people under 21 should not use any form of cannabis. [6] ## What the evidence does — and does not — prove Observational cohort studies, even very large ones, cannot by themselves prove that cannabis use causes psychiatric disorders. They can, however, document strong and consistent associations across different countries, decades, and study designs — and adjust for many of the most important confounders. [1][2][3] A 2023 genetically informed study in The Lancet Psychiatry, using data from the Psychiatric Genomics Consortium and other international cohorts, found substantial shared genetic architecture between cannabis phenotypes and psychotic disorders, with Mendelian randomisation suggesting bidirectional effects between cannabis use and bipolar disorder. [7] Taken together, the JAMA, Cambridge, and Lancet research — alongside CDC and AAP guidance — point in the same direction: earlier and more frequent cannabis use in adolescence is associated with a meaningfully higher risk of serious psychiatric outcomes in young adulthood, especially psychotic and bipolar disorders. [1][2][3][5][6][7] ## Practical takeaways for parents, teens, and clinicians - Delaying any cannabis use until at least adulthood is the position recommended by the American Academy of Pediatrics. [6] - CDC resources offer plain-language guidance on cannabis and the developing brain that parents and teens can read together. [5] - Clinicians can use NIDA's research hub to find up-to-date evidence summaries on cannabis and mental health when counselling families. [4] - Anyone experiencing symptoms such as persistent low mood, mood swings, hallucinations, or paranoia should seek evaluation from a qualified healthcare provider — these symptoms are treatable, and early intervention generally improves outcomes. [5][6] ## Sources (clickable) - [1] Young-Wolff, K.C. et al. (2026). 'Adolescent Cannabis Use and Risk of Psychotic, Bipolar, Depressive, and Anxiety Disorders.' JAMA Health Forum, published 20 February 2026. DOI: https://doi.org/10.1001/jamahealthforum.2025.6839 — https://jamanetwork.com/journals/jama-health-forum/fullarticle/2845356 - [2] Jefsen, O.H., Erlangsen, A., Nordentoft, M., Hjorthøj, C. (2023). 'Cannabis Use Disorder and Subsequent Risk of Psychotic and Nonpsychotic Unipolar Depression and Bipolar Disorder.' JAMA Psychiatry, 80(8): 803–810. DOI: https://doi.org/10.1001/jamapsychiatry.2023.1256 — https://jamanetwork.com/journals/jamapsychiatry/fullarticle/2804862 - [3] Hjorthøj, C., Compton, W., Starzer, M., Nordholm, D., Einstein, E., Erlangsen, A., Nordentoft, M., Volkow, N.D., Han, B. (2023). 'Association between cannabis use disorder and schizophrenia stronger in young males than in females.' Psychological Medicine, 53: 7322–7328. DOI: https://doi.org/10.1017/S0033291723000880 — https://www.cambridge.org/core/journals/psychological-medicine/article/association-between-cannabis-use-disorder-and-schizophrenia-stronger-in-young-males-than-in-females/E1F8F0E09C6541CB8529A326C3641A68 - [4] National Institute on Drug Abuse (NIDA), NIH — 'Young men at highest risk of schizophrenia linked with cannabis use disorder' (4 May 2023): https://nida.nih.gov/news-events/news-releases/2023/05/young-men-at-highest-risk-schizophrenia-linked-with-cannabis-use-disorder - [5] U.S. Centers for Disease Control and Prevention (CDC) — 'Cannabis and Teens' (updated 15 February 2024): https://www.cdc.gov/cannabis/health-effects/cannabis-and-teens.html - [6] American Academy of Pediatrics — 'Is Cannabis Harmful for Children & Teens? AAP Policy Explained' (HealthyChildren.org): https://www.healthychildren.org/English/ages-stages/teen/substance-abuse/Pages/legalizing-marijuana.aspx - [7] Hindley, G. et al. (2023). 'The relationship between cannabis use, schizophrenia, and bipolar disorder: a genetically informed study.' The Lancet Psychiatry, 10(6): 441–451. DOI: https://doi.org/10.1016/S2215-0366(23)00143-8 — https://www.thelancet.com/journals/lanpsy/article/PIIS2215-0366(23)00143-8/abstract --- _Canonical article: [https://brainwavepost.com/article/adolescent-cannabis-mental-health-psychosis-bipolar-2026](https://brainwavepost.com/article/adolescent-cannabis-mental-health-psychosis-bipolar-2026) — © BrainWavePost. Educational content; see the article page for full disclaimers._