Impact of Cannabis Use on Time to Psychiatric Rehospitalization in Young Adults With Bipolar and Psychotic Disorders: A Survival Analysis.

Objective: Psychiatric disorders are frequently associated with drug use and substance use disorders (SUDs). This study aimed to (1) assess the risk of psychiatric readmission associated with cannabis use in young adults (18-29 years) with bipolar or psychotic disorders and (2) describe drug use and SUD recorded in their medical files. Methods: This historical cohort included 200 adults aged 18-29 years hospitalized full time for psychotic or bipolar disorders in 2017 (index hospitalization) and followed until May 31, 2023. Data were extracted from medical records. Cox regression models assessed the association between cannabis use at admission and psychiatric readmission during the year after discharge. Results: Among the 200 patients (mean age 24 years; 47% male), 58% reported lifetime drug use and 44% current drug use at admission, excluding alcohol and tobacco. Multiple drug users represented 13%, and 37% had SUD. Cannabis was the most commonly used drug (lifetime 58%, current 43%), followed by cocaine (17% and 6%) and ecstasy (15% and 5%). Cannabis use at the index hospitalization was associated with an increased risk of readmission within the first month postdischarge (hazard ratio [HR]=2.8; 95% CI 1.3-5.9), decreasing by 3 months (HR=1.9; 95% CI 1.1-3.3), and becoming nonsignificant at 6 months. Conclusion: In young adults with psychotic or bipolar disorders, cannabis use at admission is a significant predictor of early psychiatric readmission. The first 3 months postdischarge represents a critical period for targeted follow-up and intervention.