State-level legalization of cannabis has been linked to a sharp rise in use among those with psychosis, a new study showed.

Among those with psychosis, past-month cannabis use increased by 9.53 percentage points in states with legal recreational use. No changes were identified for weekly or more frequent cannabis use among this population.

“Given how cannabis can negatively affect illness course and health service utilization in individuals with psychosis, these results should be considered by regulators designing policies around taxation, potency, advertising, and health warnings,” the investigators, with first author, Andrew S. Hyatt, MD, Department of Psychiatry, Harvard Medical School, Boston, wrote.

The study was published online on October 8 in JAMA Psychiatry.

Increased Psychosis Risk

To date, 24 states have legalized cannabis for recreational use. The growing commercialization of the drug is “a cause for concern” for individuals with psychosis who have experience higher symptom burden and relapse rates than nonusers, the investigators noted.

Previous studies have shown that cannabis use is associated with an increased risk for psychosis. However, this study is the first to investigate how recreational legalization affects cannabis use in those with psychosis.

Investigators analyzed data from the Population Assessment of Tobacco and Health study from 2014 to 2022. The study sample consisted of 1856 individuals (mean age, 36.6 years, 50.2% White, 58.2% female) who reported a diagnosis of psychosis or psychotic disorder.

Difference-in-differences models were used to assess changes in cannabis use associated with recreational legalization. States that have not legalized cannabis were the reference group for the analysis.

Further sensitivity analyses were used to evaluate changes in cannabis use before and after retail outlets opened, as well as for more frequent use and legal age restrictions.

Call for Regulatory Action

After adjusting for covariates including race, ethnicity, receipt of antipoverty assistance, sex, and age, past-month cannabis use in individuals with psychosis rose after legalization by 9.53 percentage points (95% CI, 3.05-16.00; P = .004).

Similar results were obtained when the analysis was restricted to those aged 21 or above.

“Current cannabis use did not significantly increase before the retail outlets opened but did increase significantly afterward,” the investigators wrote. The increase was 10.51 percentage points (95% CI, 3.56-17.46). They found no significant changes for more frequent or weekly cannabis use.

A limitation of the study was that psychosis diagnoses were self-reported. In addition, the sample size consisted of a higher number of women than other studies of people with psychosis which could restrict generalizability.

Health warnings on cannabis products for those with a history of psychosis and taxation by potency could help prevent negative impacts on this population, the researchers suggested.

The authors reported no disclosures. This work was supported by grants K23DA062173 (Hyatt) and R01DA060795 (Flores) from the National Institute on Drug Abuse as well as grant P50MH126283 (Flores, Cook) from the National Institute on Mental Health.