Cannabis and Psychosis Risk: How Legalization Could Impact Clinical Practice

What does cannabis legalization mean for psychosis risk?

A young man once sat across from me, hollow-eyed, trembling, and frightened. He had tapered off his psychiatric medication and started using cannabis to help him sleep. At first, he said it worked. Then it did not. Soon he could no longer tell what was real.

This story is not uncommon. Some patients present with paranoia, panic, mood instability, perceptual disturbance, or a first psychotic break. Many are young. Many are using increasingly potent cannabis products. As legalization expands, clinicians are increasingly asked to manage a widening gap between public perception and psychiatric risk.

The question is no longer simply whether cannabis should be legal. It is whether legalization has encouraged a more dangerous assumption: that cannabis is safe because its use is legal, or harmless enough to normalize. From a psychiatric standpoint, that assumption is becoming harder to sustain.

Cannabis is now deeply woven into the American commercial landscape. State-legal sales have surged, tax revenue has become politically attractive, and public support for legalization continues to rise.^1-3 But while the policy environment has changed rapidly, the psychiatric literature has become more, not less, cautionary.

The Strongest Recent Cohort Data

One of the most important recent studies comes from a large longitudinal cohort published in JAMA Health Forum.⁴ Investigators followed 463,396 adolescents aged 13 to 17 years who were universally screened for past-year cannabis use during routine pediatric care and then tracked through age 25 years or the end of follow-up—a notable sample size. It gives the study unusual statistical power and makes it harder to dismiss the findings as noise.

The results were striking. Adolescents who reported past-year cannabis use had increased risk of several psychiatric diagnoses, but the strongest associations were with psychotic disorder and bipolar disorder.⁴ In the primary model, past-year cannabis use was associated with an adjusted hazard ratio (HR) of 2.19 for psychotic disorder and 2.01 for bipolar disorder. Associations were also seen for depressive disorders (HR, 1.34) and anxiety disorders (HR, 1.24).⁴

Even after investigators adjusted for prior psychiatric conditions, the association remained robust: 1.92 for psychotic disorder and 1.73 for bipolar disorder.⁴ That matters because one of the most common objections in this area is reverse causation, or the idea that young people with emerging psychiatric symptoms may simply be more likely to use cannabis. That concern is legitimate. But when associations remain significant even after accounting for baseline psychiatric illness and other substance use, the argument that this is entirely explained away becomes much weaker.

The timing is also notable. Among adolescents who later developed psychiatric diagnoses, the mean time from first reported cannabis use to diagnosis ranged from roughly 1.7 to 2.3 years.⁴ That does not prove causality, but it does suggest that the interval between exposure and clinical consequence may be shorter than many assume. The study is also important because it used a relatively crude exposure measure, simply whether the adolescent had reported cannabis use in the past year. In other words, this was not a study limited to heavy daily users or narrowly defined cannabis use disorder. A signal emerged even with a broad screening measure.⁴

Psychosis

If there is one domain in which the evidence is most consistent, it is psychosis. The EU-GEI multicenter case-control study published in The Lancet Psychiatry remains one of the most cited papers in this debate.⁶ It examined patients with first-episode psychosis and controls across multiple European sites, and found that daily cannabis use was associated with an odds ratio of 3.2 for psychotic disorder, while daily use of high-potency cannabis was associated with an odds ratio of 4.8.⁶

What makes this paper so clinically useful is that it moves the conversation beyond the vague question of whether cannabis is “good” or “bad” and toward a more psychiatric formulation: which exposure, in whom, and how much? The study suggests that frequency and potency matter substantially. That distinction is essential in current practice, because today’s cannabis marketplace is not just more legal. It is more potent, more diverse, and more engineered for repeated high-dose exposure.

A broader review in World Psychiatry reinforces this point.⁵ The authors summarize evidence that cannabis use is linked to increased psychotic outcomes, that the association follows a dose-response pattern, and that high-potency cannabis and synthetic cannabinoids carry the greatest risk.⁵ The review also cites evidence that daily users of high-potency cannabis may experience a first episode of psychosis about 6 years earlier than those who have never used.⁵ Even if one remains cautious about making strong causal claims, earlier onset in vulnerable individuals is a clinically meaningful outcome.

Mood and Suicidality Outcomes

Psychosis tends to dominate the discussion, but mood outcomes should not be ignored. A 2019 JAMA Psychiatry systematic review and meta-analysis by Gobbi et al pooled longitudinal studies examining adolescent cannabis use and later mood and suicidality outcomes.⁷ Eleven studies met criteria. The pooled data showed that adolescent cannabis use was associated with increased odds of later developing depression, anxiety, suicidal ideation, and suicide attempts, although the magnitude of risk varied.

Among the most important findings, adolescent cannabis use was associated with an odds ratio of 1.50 for suicidal ideation and an odds ratio of 3.46 for suicide attempt.⁷ The confidence interval around suicide attempt was wide, but the effect size is still difficult to ignore. The paper’s results for depression also suggested a meaningful increase in later risk.⁷ This does not mean cannabis is a singular cause of depression or suicidality, only that adolescent exposure appears to be associated with worse later outcomes at the population level.

For psychiatrists, this matters because cannabis use is often framed by patients as self-medication for anxiety, insomnia, or dysphoria. Some patients do experience short-term subjective relief. But the literature suggests that short-term perceived benefit does not reliably predict long-term psychiatric safety, especially in adolescents and young adults.

Cannabis-Induced Psychosis

One reason clinicians should take cannabis-related psychiatric presentations seriously is that they do not always resolve into harmless, isolated episodes. The Acta Psychiatrica Scandinavica review by Baandrup summarizes several sobering figures.⁸ It notes a more than 2-fold increase in the incidence rate of cannabis-induced psychosis in Denmark, from 2.8 per 100,000 person-years in 2006 to 6.1 per 100,000 person-years in 2016.⁸ Even more striking, the review cites data showing that 47.7% of individuals with cannabis-induced psychosis in Denmark converted to either schizophrenia or bipolar disorder over follow-up.⁸

That figure is clinically important because it counters a common minimizing narrative: that cannabis-related psychosis is usually brief, self-limited, and of little long-term significance. In reality, for a substantial subset of patients, it may be an early marker of enduring severe mental illness rather than a transient toxic state.⁸

Population-Level Signals

At the population level, the association between cannabis use disorder and schizophrenia has become harder to ignore. The Danish study by Hjorthøj et al found that the proportion of schizophrenia cases associated with cannabis use disorder was especially pronounced among young men.⁹ The implication is not that cannabis use disorder explains most schizophrenia, but that at a population level it may account for a meaningful fraction of incident cases in high-risk groups.⁹

Ontario data point in a similar direction. In a JAMA Network Open study, the proportion of incident schizophrenia cases associated with cannabis use disorder increased over time and was higher in the period after legalization, with younger men again showing the greatest signal.¹⁰ These ecological and population-level data cannot establish that legalization itself caused the increase, but they do suggest that a broader commercial exposure environment may not be psychiatrically neutral.

Potency

This discussion becomes even more urgent when potency enters the frame. The cannabis many adults remember from decades ago is not the product many adolescents and young adults encounter now. The National Institute on Drug Abuse notes that average tetrahydrocannabinol concentrations have increased substantially over time, while concentrates, edibles, and other newer formulations can deliver far higher exposure than older cannabis products.¹¹ The CDC similarly warns that cannabis use before age 18 may affect memory, attention, learning, and brain health, though the full long-term effects are still being clarified.¹²

For psychiatry, potency is not a side detail. It may be one of the central variables linking legalization-era cannabis to more severe psychiatric presentations. When a patient says they “use cannabis,” that statement now spans a spectrum from intermittent low-potency exposure to repeated use of very high-potency products. Those are not interchangeable risks.

What Psychiatrists Should Do With This Evidence

The lesson for clinicians is not moral panic; It is precision. Cannabis history should be part of routine psychiatric assessment, especially in adolescents, young adults, and patients presenting with anxiety, affective instability, attenuated psychotic symptoms, or first-episode psychosis. Asking only whether a patient uses cannabis is no longer enough. We should ask how often, at what age use began, in what form, at what potency, and with what perceived benefits or harms.

Patients also deserve clearer counseling. The right message is not that cannabis risk is all-or-none. It is that risk appears to rise along lines the literature repeatedly identifies: younger age of exposure, heavier or daily use, higher potency, and vulnerability to psychosis-spectrum illness.^5-8 For patients with personal or family histories of psychosis, bipolar disorder, or severe mood instability, that counseling becomes even more important.

Psychiatry should also be able to hold 2 ideas at once. One can oppose overly punitive criminalization and still acknowledge that normalized, commercialized, high-potency cannabis exposure may carry real psychiatric consequences. Those positions are not contradictory. Responsible public health policy requires both. Cannabis may now be legal across much of the United States. It may be profitable, packaged, and culturally normalized, but it is not harmless.

Dr Taj is an assistant professor of psychiatry at Case Western Reserve Medical School. He is also a senior attending physician of psych-oncology at the Seidman Cancer Center in the Division of Consultation-Liaison Psychiatry, the Department of Psychiatry, at University Hospitals of Cleveland.

References

1. Krawiec S. 2025 state of the cannabis industry: sales trends and forecasts. Cannabis Science and Technology. December 23, 2025. Accessed April 30, 2026. https://www.cannabissciencetech.com/view/2025-state-of-the-cannabis-industry-sales-trends-and-forecasts

2. Cannabis tax revenue in states that regulate cannabis for adult use. Marijuana Policy Project. May 17, 2025. Accessed April 30, 2026. https://www.mpp.org/assets/pdf/issues/legalization/cannabis-tax-revenue-states-regulate-cannabis-adult-use.pdf?v=1766967271

3. Brenan M. Support for legal marijuana inches up to new high of 68%. Gallup. November 9, 2020. Accessed April 30, 2026. https://news.gallup.com/poll/323582/support-legal-marijuana-inches-new-high.aspx

4. Young-Wolff KC, Cortez CA, Alexeeff SE, et al. Adolescent cannabis use and risk of psychotic, bipolar, depressive, and anxiety disorders. JAMA Health Forum. 2026;7(2):e256839.

5. Murray RM, Quigley H, Quattrone D, et al. Traditional marijuana, high-potency cannabis and synthetic cannabinoids: increasing risk for psychosis. World Psychiatry. 2016;15(3):195-204.

6. Di Forti M, Quattrone D, Freeman TP, et al. The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study. Lancet Psychiatry. 2019;6(5):427-436.

7. Gobbi G, Atkin T, Zytynski T, et al. Association of cannabis use in adolescence and risk of depression, anxiety, and suicidality in young adulthood: a systematic review and meta-analysis. JAMA Psychiatry. 2019;76(4):426-434.

8. Baandrup L. Managing the hazards of cannabis use. Acta Psychiatr Scand. 2022;145(3):231-233.

9. Hjorthøj C, Compton W, Starzer M, et al. Association between cannabis use disorder and schizophrenia stronger in young males than in females. Psychol Med. 2023;53(16):7322-7328.

10. Myran DT, Pugliese M, Harrison LD, et al. Changes in incident schizophrenia diagnoses associated with cannabis use disorder after cannabis legalization. JAMA Network Open. 2025;8(2):e2457868.

11. Cannabis (marijuana) research report. National Institute on Drug Abuse. July 2020. Accessed April 30, 2026. https://www.drugsandalcohol.ie/37727/1/cannabis-marijuana-research-report.pdf

12. Cannabis and brain health. Centers for Disease Control and Prevention. February 15, 2024. Accessed April 30, 2026. https://www.cdc.gov/cannabis/health-effects/brain-health.html