Patients hospitalized for major depressive disorder who tested positive for THC were no more likely to be readmitted within 30 days or experience longer hospital stays than those who tested negative, according to a new study published in Brain and Behavior.
Researchers from the Ernest Mario School of Pharmacy at Rutgers University and St. Joseph’s University Medical Center examined 743 psychiatric hospital admissions involving adults with major depressive disorder. Of those cases, 211, or 28.4%, tested positive for THC upon admission.
The retrospective study included patients discharged from an inpatient psychiatric unit between August 2018 and May 2025. All participants had a diagnosis of major depressive disorder, underwent a urine drug screen and received at least one antidepressant during their hospitalization and at discharge. Patients with bipolar disorder, schizophrenia and schizoaffective disorder were among those excluded.
Researchers primarily examined whether THC-positive patients were more likely to return for psychiatric hospitalization within 30 days and whether they spent more time hospitalized.
Thirty-day readmission rates were nearly identical between the groups. Seven THC-positive cases, or 3.3%, resulted in readmission within 30 days, compared with 19 cases, or 3.6%, among patients who tested negative for THC.
After researchers adjusted for age, gender at birth, psychiatric comorbidities and polysubstance use, THC status remained unrelated to 30-day readmission risk. The adjusted odds ratio was 0.821, with the difference falling well short of statistical significance.
The study initially found that THC-positive patients had somewhat shorter hospital stays. Their average hospitalization lasted 5.26 days, compared with 5.98 days among THC-negative patients, a difference of approximately 0.7 days that was statistically significant in the unadjusted analysis.
However, that difference disappeared after accounting for other patient characteristics. In the adjusted analysis, THC positivity was associated with a 0.242-day shorter stay, but the result was not statistically significant.
Researchers also examined longer-term readmissions. Within six months, 5.2% of THC-positive cases had been readmitted compared with 7.9% of THC-negative cases. Between six months and one year, the rates were 3.3% and 4.5%, respectively. Neither difference reached statistical significance.
The researchers said the findings suggest THC exposure, as measured by a positive urine test, was not independently associated with worse hospitalization outcomes among patients with major depressive disorder.
Several limitations were noted by the study’s researchers. The research was conducted at a single medical center and was retrospective, limiting how broadly the results can be applied. Researchers also lacked information about the amount of THC consumed, frequency of marijuana use, product formulation or duration of use. A positive urine test therefore identified THC exposure but did not distinguish occasional from frequent or heavy marijuana use.
In addition, the analysis was conducted by hospitalization rather than individual patient, meaning some people could contribute more than one case if their hospitalizations occurred more than a year apart.
The researchers concluded that larger, multicenter studies with more detailed information on THC dose, frequency and formulation are needed to determine whether particular patterns of marijuana use affect psychiatric hospitalization outcomes among people with major depressive disorder.
