What impact has legalization and commercialization of recreational cannabis had on people with schizophrenia and other disorders involving psychosis?

It’s an important question, particularly in view of published studies reporting that those with psychotic disorders who use cannabis, on average, “have a higher symptom burden, worse functioning, more and longer hospitalizations, and higher relapse rates compared with non-users.”

This observation, made by authors of a new study appearing in JAMA Psychiatry, motivated their effort to learn how legalization and commercialization may be affecting this population, which they regard as vulnerable, “especially given the rapid increase in market share of high-potency [cannabis] products.” Such products, which can have many times the THC content of cannabis typically sold on the streets illegally several decades ago, have been flagged by the National Institute on Drug Abuse (NIDA) and its Director, Nora D. Volkow, M.D., as posing particularly important perils for those with psychosis and possibly also those who are at high-risk for psychotic disorder (due to genetics and family history). Dr. Volkow is a member of BBRF’s Scientific Council.

“No study, to our knowledge, has quantified whether patterns of cannabis use in individuals with psychotic disorders changed following state-level legalization and commercialization of cannabis,” wrote the team, which was led by Andrew S. Hyatt, M.D., of Harvard Medical School. Dost Öngür, M.D., Ph.D., a BBRF Scientific Council member, 2013 BBRF Independent Investigator and 2004 Young Investigator, and Anne Eden Evins, M.D., MPH, a 1999 and 1996 BBRF Young Investigator, were members of the team.

The researchers used data from an ongoing study administered by NIDA and the Food and Drug Administration called PATH (Population Assessment of Tobacco and Health) which is following a large cohort of Americans over time. The study collects individual-level data on substance use and health conditions and is the only nationally representative study of substance use that gathers such information over time about people diagnosed with psychosis.

Of the over 56,000 people who have participated in PATH, the team used data from the years 2014 to 2022 to form a cohort of 1,856 individuals who reported a diagnosis of psychosis or a psychotic disorder at some point in their life. About half were white, 58% were female, and the median age was about 36. Some were cannabis users, others were not. Some lived in a state that had legalized cannabis, others did not. The study made it possible to compare those who lived in “legalization” states and used cannabis with those who used cannabis but lived in states that had not legalized it, as well as usage rates pre- and post-legalization.

For purposes of the study, “legalization” meant enactment of a law legalizing adult possession of nonmedical cannabis and directing the establishment of commercial retail markets. User assessment was studied at 5 years post-legalization.

Results of the analysis indicated that cannabis use among individuals with a history of psychosis “sharply increased” in states where recreational cannabis was legalized. The actual figure was an increase in cannabis use over the prior 30 days of 9.53%, compared with pre-legalization responses. This was based on 7,465 responses to the question of prior 30-day use by the 1,856 individuals in the cohort over a period of years. The figure of increased use following legalization compares with a 3.3% increase in prior 30-day use among the general population.

Because of the longitudinal nature of the dataset, it was possible for the team to note that the increase in 30-day use among those with psychosis history occurred after cannabis commercialization in a given state. That is, the increase did not appear to correlate with passage of a law, but rather with greater availability of commercial cannabis that attended actual commercialization.

“Commercialization has increased exposure to advertising containing cannabis-related mental health claims” the researchers noted, and few states require specific warnings about mental health harms, with only 2 states [Colorado and Connecticut] requiring warnings about the link between cannabis and psychosis.”

The increase in prior 30-day cannabis use among those with psychosis history, while “cause for concern,” is of uncertain impact, the team said. “It is not yet known if this will translate into negative health consequences.” Legalization was associated with more occasional (past-month) use, but not with more weekly use “which may limit negative effects.” On the other hand, the “large increase in market share of high-potency products in states that have legalized and commercialized cannabis could render occasional use more harmful to individuals with psychosis.”

To mitigate possible negative impacts, the team suggested that regulators consider including health warnings on cannabis packaging, noting the particular risk for those with a family or personal history of psychosis. Regulators might also, they said, examine mental-health claims in cannabis advertising. Potency caps on products might also be considered, perhaps via a tax assessed on the basis of potency, they suggested.

As for future studies, it will be important to collect, as this study could not, data on treatment history, symptom burden, and comorbidity for those in the study cohort, as well as data on cannabis potency among those who use the drug, “given the strong association between worsening psychosis and high-potency cannabis product use.”