Psychosis and Cannabis Legalization: Where’s the Evidence?

Just what impact nationwide cannabis policy changes might have on psychosis remains unclear, with mixed and emerging data from the studies that have been done, preliminary findings of a systematic review indicated.

Across the 33 studies reviewed, cannabis dose and age at first use appeared to play a role in the risk for psychosis, Jeonghyun Shin, MD, MPH, of Maimonides Medical Center in New York City, said at the American Psychiatric Association annual meeting in San Francisco.

For example, one study linked daily use of high-potency cannabis (>10% tetrahydrocannabinol [THC]) to a nearly five-fold increase in the odds of developing a psychotic disorder compared with never-users (adjusted OR 4.8, 95% CI 2.5-6.3). Another study tied cannabis use starting by 15 years of age to an earlier onset of psychosis compared with those who started later.

While signals have emerged in some studies, other data on state policies legalizing cannabis and psychosis-related outcomes have turned up null results. Shin called this a “critical” research gap that requires further study.

“There has been emerging evidence showing that there’s a link between cannabis use and the risk of psychosis,” said Shin. “Because there’s been so much rapid change in the policy and this emerging evidence, researchers have started to look into whether these policy changes actually impact psychosis.”

Currently, the Trump administration is in the process of rescheduling cannabis. In April, state-licensed medical marijuana was reclassified from a Schedule I substance — reserved for drugs without medical use and with high potential for abuse — to the less strictly regulated Schedule III. The order also eased some barriers around researching cannabis.

This shift did not apply to recreational cannabis. The Drug Enforcement Agency plans to hold an administrative hearing in June to determine the rule for a broader, more complete rescheduling of cannabis. Today, cannabis policy varies from state to state, ranging from decriminalization, medical legalization, and recreational legalization all the way to commercialization.

Some data don’t quite match up with what is being seen in clinical practice, added co-author Jamie Baik, MD, MEd, of Cambridge Health Alliance in Massachusetts. “I’m sure all of us in practice can say something about cannabis making outcomes and symptoms a lot worse, but it’s somehow not being reflected in the data immediately.”

Baik also suggested that these policy changes may be impacting young adults more than teens.

“The transitional-age youth group that we originally focused on is 15 to 25, but studies are showing that adolescents up until age 18 or 19 were not actually showing a greater use in cannabis after legalization occurred ,” she explained. Instead, “young adults 19 to 25 were disproportionately affected. But when they all get lumped together, you don’t get anything significant.”

For the systematic review, Shin’s group searched four research databases and reviewed literature published through January 2026. Peer-reviewed studies on THC, cannabis, and synthetic cannabinoids were included.

Of the 33 studies included, 11 looked at cannabis use among individuals who had psychosis or who were at high risk for it, and 17 looked at either emergency department visits associated with psychosis or psychosis-related inpatient hospitalizations. Most (n=21) looked at the general population, but 12 looked specifically at outcomes in youth ages 15-25.

For the next steps, Shin said her team looks forward to extracting the data and making more definitive conclusions regarding different outcomes and different age groups, as well as providing more insights into policy. “The biggest question everyone might have would be … did policy change actually impact psychosis? Our short answer would be that we don’t know as of yet,” she said. “Stay tuned for the final results.”