High‑THC Cannabis Associated With Rapid Onset Psychosis, Review Finds

A large review of published research has found an association between high‑potency cannabis products and short‑term onset of psychosis, including symptoms that led to emergency care and, in some cases, progression to schizophrenia.

Researchers from institutions in Massachusetts and Colorado reviewed 99 studies that included 221,097 cannabis users and focused on products containing at least 5 milligrams of tetrahydrocannabinol (THC) or more than 10 percent THC per serving. Seventy percent of the studies reported an unfavorable link between such high‑THC products and psychosis or schizophrenia, and the association was often identified within the first 12 hours after use and persisted in follow‑up periods of up to two months.

The analysis found most studies examined adults aged 18 to 59; 4 percent included adolescents. The investigators did not consistently report how frequency of use affected the timing of mental health outcomes. Lead author Jonathan Samet, a professor of epidemiology and environmental and occupational health at the Colorado School of Public Health, said the findings "are concerning and warrant a precautionary approach to using cannabis products, particularly for those with preexisting psychosis."

Public‑health experts and researchers have pointed to two broad trends that may be driving the observed risks: sharply rising population use and dramatically increased potency of cannabis available in legal and illicit markets. In the United States, self‑reported cannabis use nearly doubled in a decade, rising to 21.8 percent of people age 12 and older — about 61.8 million individuals — in 2023, up from 12.6 percent in 2013. Average THC content in seized smokable cannabis rose from about 4 percent in 1995 to roughly 20 to 30 percent in recent retail samples; THC concentrations in some vaping and concentrate products can reach the 80 to 90 percent range.

The review found differing effects of cannabis across therapeutic and nontherapeutic contexts. In nontherapeutic studies, 53 percent reported worsening anxiety and 41 percent reported worsening depression; participants with no underlying conditions appeared most vulnerable to these effects. In therapeutic trials, participants reported relief from anxiety or depression in about half of the studies, with patients with cancer and certain neurologic conditions reporting the most benefit.

The investigators also reported widespread evidence of cannabis dependence: 75 percent of the studies were associated with development of cannabis use disorder, a condition in which use continues despite significant impairment or distress. National surveys suggest the prevalence of cannabis use disorder has risen alongside broader increases in use; the review noted that nearly one‑third of people who used cannabis in 2023 met criteria for the disorder.

The new review aligns with other recent research linking acute cannabis‑related hospital care to elevated risks of longer‑term psychotic disorders. A separate study published last month in the Canadian Medical Association Journal found that patients hospitalized for cannabis‑related health problems were 14 times more likely to develop schizophrenia within three years than comparison patients. That study reported an especially high relative risk — 241 times higher — for schizophrenia among people hospitalized for cannabis‑induced psychosis. Researchers described cannabis‑induced psychosis as a temporary condition involving hallucinations, delusions and disorganized thinking; many patients who experience symptoms lasting more than 24 hours require emergency care.

Experts quoted in the broader literature emphasize that the rise in severe psychiatric outcomes appears linked to higher THC concentrations. "Cannabis from the 2000s is not the same as in 2025," said Nicholas Fabiano of the University of Ottawa, noting changes in product potency and formulation.

The review and related reporting have highlighted individual cases that illustrate extreme outcomes. In a criminal trial last year, prosecutors and expert witnesses described a defendant whose actions were attributed in part to an episode of severe psychosis that they said followed use of potent cannabis. Court testimony in that case included statements by a forensic psychiatrist that the defendant had no prior history of mental illness or violence and that the psychotic episode occurred after consuming high‑potency marijuana. The defendant was convicted of homicide; court records show testimony and evidence were evaluated by jurors in determining culpability.

Policy changes that have increased access to cannabis are likely influencing population exposure to high‑THC products. Recreational use is fully legal in 24 states and the District of Columbia; more than half of Americans live in states where recreational cannabis is legal, and Pew Research Center data indicate 79 percent of Americans live in a county with at least one dispensary. Advocates and clinicians disagree about how legalization affects harms, but regulators have not uniformly set potency limits across jurisdictions.

Medical uses of cannabis — including treatment of chronic pain, chemotherapy‑related nausea and some forms of epilepsy — were represented among the reviewed studies and in clinical practice, and therapeutic trials produced mixed results for mood‑related symptoms. Treatment for schizophrenia and other psychotic disorders remains pharmacologic and psychosocial, with antipsychotic medications and cognitive behavioral approaches used to manage symptoms and improve functioning.

The authors of the review and other public‑health specialists urged caution, improved communication about risks associated with high‑potency products, and additional research to clarify how dose, formulation, age at first use and frequency of consumption influence outcomes. Regulators and clinicians may consider those factors when advising patients or setting product standards, the researchers said, while noting that evidence continues to emerge about long‑term mental health effects of widely available cannabis products.