A landmark population study involving nearly half a million teenagers has found that adolescent marijuana use is associated with more than double the risk of developing two of the most serious mental illnesses known — psychotic disorders and bipolar disorder — by young adulthood.
The research, published in JAMA Health Forum on February 20, 2026, tracked 463,396 adolescents aged 13 to 17 through age 26 using electronic health record data from Kaiser Permanente Northern California. It represents one of the largest longitudinal studies of its kind ever conducted on adolescent cannabis use and psychiatric outcomes.
The findings arrive at a moment when cannabis is more potent, more widely marketed, and more legally accessible to adolescents than at any point in American history — making the clinical implications both significant and timely.
Why This Matters
Psychotic disorders — which include schizophrenia and related conditions involving breaks from reality — and bipolar disorder are among the most disabling mental illnesses a person can develop. They typically require lifelong treatment, are expensive to manage, carry high rates of hospitalization and unemployment, and substantially reduce quality of life.
The U.S. cannabis market is valued in the tens of billions of dollars, with sophisticated marketing and expanding retail availability. Meanwhile, more than 10% of 12- to 17-year-olds in the United States report past-year cannabis use. By senior year of high school, approximately 26% of American teenagers have used marijuana at least once.
The JAMA study suggests that for a meaningful fraction of those adolescents — those who are genetically or neurobiologically predisposed — that exposure may trigger or accelerate a psychiatric trajectory that would not have occurred, or would have occurred later, without the drug.
What We Know So Far
The study's design is one of its key strengths. Researchers analyzed universal screening data from routine pediatric visits at Kaiser Permanente Northern California between 2016 and 2023. Unlike studies that rely on self-selected cohorts or retrospective self-report, this design captured cannabis use data from nearly all adolescents receiving routine care within a large, defined health system.
Key findings, published in JAMA Health Forum (DOI: 10.1001/jamahealthforum.2025.6839):
- Past-year cannabis use was associated with double the risk of developing psychotic disorders by age 26
- Past-year cannabis use was associated with double the risk of developing bipolar disorder by age 26
- Significant increases were also found in the risk of depressive and anxiety disorders
- Cannabis use preceded psychiatric diagnoses by an average of 1.7 to 2.3 years — a timeline consistent with a causal relationship
- The association remained significant after researchers adjusted for other substance use and pre-existing mental health conditions
Approximately 4,000 out of the 463,396 teens in the study were ultimately diagnosed with psychotic disorders, and a similar number with bipolar disorder. Those raw numbers seem small, but represent a substantial population given the study size.
Where the Risk Is Highest
Adolescents face the highest risk in states where cannabis has been legalized and where THC-potency regulations are limited. Modern commercially sold cannabis products are dramatically more potent than cannabis from prior decades. THC content in cannabis flowers sold in California now routinely exceeds 20%, while concentrates can reach 95% — compared to less than 4% THC in cannabis products of the 1980s.
Youth in states with recreational cannabis availability — including California, Colorado, Washington, Oregon, Michigan, Illinois, New York, and others — are more likely to encounter high-potency products that amplify the neurobiological risk identified in this research. Adolescents whose families live near retail cannabis dispensaries and in states without strong age-verification enforcement face compounded exposure.
What Doctors and Experts Say
"As cannabis becomes more potent and aggressively marketed, this study indicates that adolescent cannabis use is associated with double the risk of incident psychotic and bipolar disorders, two of the most serious mental health conditions," said Dr. Lynn Silver, a program director at the Public Health Institute in Oakland, California, and a co-author of the study.
"This is very, very, very worrying," said Dr. Ryan Sultan, a psychiatrist and cannabis researcher at Columbia University who was not involved in the study, in an interview with NPR. Sultan added that psychotic and bipolar disorders represent "the scarier conditions that we worry about," noting that the societal cost of schizophrenia alone has been estimated at approximately $350 billion annually.
Researchers noted that the study's longitudinal design — which showed cannabis use typically preceding psychiatric diagnosis by nearly two years — strengthens the case for cannabis exposure as a potential risk factor, not merely a correlate.
What the Evidence Shows — and What It Does Not
This is an observational cohort study — it identifies strong associations but cannot definitively prove that cannabis caused the psychiatric diagnoses. Researchers acknowledged that some adolescents may have used cannabis in part to address emerging, not-yet-diagnosed mental health symptoms (a pathway sometimes called "self-medication"), which would create a correlation without direct causation.
However, the study's lead researchers noted two features that strengthen a causal interpretation: the average 1.7 to 2.3-year gap between cannabis use and diagnosis (suggesting cannabis came first), and the fact that the association remained significant after controlling for other substance use and pre-existing mental health conditions.
The study cannot determine which individual adolescent cannabis users will develop psychiatric illness. The doubled risk reflects a population-level probability. Many adolescents who use cannabis will not develop psychosis or bipolar disorder — but the population of those who will is substantially larger than among non-users.
MedicalDaily Evidence Check
- Study type : Longitudinal cohort study (observational)
- Participants : 463,396 adolescents aged 13–17 tracked through age 26
- Published in : JAMA Health Forum (February 20, 2026)
- Institutions : Kaiser Permanente, Public Health Institute, UC San Francisco, UC Southern California; funded by NIH/NIDA
- What it found : Past-year cannabis use associated with 2x risk of psychotic and bipolar disorders; cannabis typically preceded diagnosis by 1.7–2.3 years
- What it did not prove : A definitive causal link; the study cannot rule out reverse causation (self-medication of emerging symptoms)
- Key strength : Universal screening (not self-selected sample); largest cohort study of this design to date
- What readers should know : The risk is at a population level; not every teen who uses cannabis will develop psychiatric illness, but the association is strong, and the timing suggests it is not merely coincidental
Who Faces the Greatest Risk?
Adolescents most likely to be affected by this association include:
- Teenagers with a family history of psychosis, bipolar disorder, or schizophrenia (genetic loading significantly multiplies risk)
- Adolescents who begin using cannabis at a younger age (earlier initiation corresponds to more exposure during a critical brain development window)
- Teens using high-potency THC products — concentrates, edibles, and vapes with high THC percentages
- Adolescents who use cannabis frequently rather than occasionally
- Youth in states with high-availability, high-potency commercial cannabis markets
Symptoms and Warning Signs to Watch For
Parents and healthcare providers should be alert to early warning signs that can appear before a full psychiatric diagnosis:
- Social withdrawal or loss of interest in previously enjoyed activities
- Decline in school performance or attendance
- Unusual suspiciousness or paranoia
- Talking or writing about unusual beliefs not shared by others
- Disturbed sleep or changes in daily routine
- Hearing or seeing things others do not
- Sudden, marked change in mood or energy (elevated or deeply depressed)
- Rapid shifts between very high and very low emotional states
If these symptoms emerge in an adolescent — particularly one who uses cannabis — seek evaluation from a child or adolescent psychiatrist. Early intervention in psychotic and bipolar disorders substantially improves long-term outcomes.
What You Can Do Now
- Talk with your teenager about cannabis — not from a moralistic framing, but from a health-evidence framing. This study gives parents and pediatricians real data to share.
- Pediatricians should routinely screen for cannabis use at annual and well-child visits, consistent with the American Academy of Pediatrics guidance.
- If your teen is using cannabis , discuss the specific risk implications — the brain is still developing through the mid-20s, and the endocannabinoid system targeted by THC plays a direct role in brain development during adolescence.
- Know your state's cannabis laws and age-verification requirements. Advocate for strong youth access prevention measures in your community.
- Seek a psychiatric evaluation if your teenager who uses cannabis begins showing early warning signs of psychosis or mood disorder.
Cost and Access: What Patients Should Know
Child and adolescent psychiatry services are in critically short supply across the United States. Wait times for appointments may be weeks to months in many areas. If you are concerned about a teenager's mental health, the SAMHSA National Helpline (1-800-662-4357) can provide referrals to local mental health services at no cost, 24 hours a day.
Many pediatricians and family medicine physicians can perform initial mental health screenings and provide referrals. School counselors can also initiate referral pathways to community mental health resources.
What Happens Next
Researchers have stated that the findings highlight the importance of effective public health messaging and policy development to limit youth exposure as cannabis becomes more commercially available. The study is expected to inform discussions about age verification requirements, potency caps on retail cannabis products, and warning label requirements in states with legal cannabis markets.
The NIH's National Institute on Drug Abuse funded this research. Additional longitudinal follow-up studies are expected as the cohort ages into their 30s.
The Bottom Line
The largest longitudinal study of adolescent cannabis use and psychiatric outcomes ever conducted has found that teen marijuana use is associated with double the risk of developing psychosis and bipolar disorder by young adulthood. The research does not prove causation and does not predict outcomes for any individual teenager — but it establishes one of the most important population-level mental health risk associations documented in recent years. As cannabis becomes more potent and more legally available, the conversation between parents, pediatricians, and teenagers about what that risk means has never been more important.
