Co‑occurring mental and substance use disorders among residents of Drug Addiction Rehabilitation Centers (DARCs) in Japan: Characterizing dual‑diagnosis profiles.

Aim: The co-occurrence of substance use and mental disorders, commonly referred to as a dual diagnosis, presents considerable challenges to the recovery process. Despite its clinical relevance, only a few studies have examined the characteristics correlated with dual diagnoses among individuals utilizing rehabilitation services. Thus, in this study, we aimed to identify the factors associated with dual diagnoses in study participants receiving care at drug rehabilitation support facilities. Methods: We analyzed data from participants receiving care at drug rehabilitation support facilities, specifically the Drug Addiction Rehabilitation Centers. Multivariable logistic regression analysis was performed to examine the correlations among dual diagnoses and sociodemographic characteristics, facility utilization patterns, substance dependence, physical health, and recovery outcomes at the 1-year follow-up. Results: Dual diagnosis was notably correlated with the female sex (adjusted odds ratio [AOR] = 4.18, 95% confidence interval [CI]: 2.01-8.67), history of incarceration (AOR = 2.10, 95% CI: 1.35-3.28), and prior treatment for substance use disorder (AOR = 2.22, 95% CI: 1.30-3.91). At the 1-year follow-up, participants with dual diagnoses exhibited poor recovery outcomes across multiple domains; they were more likely to be unemployed (AOR = 2.10, 95% CI: 1.35-3.31) and had greater difficulty maintaining drug abstinence (AOR = 1.85, 95% CI: 1.17-2.94). Conclusion: Individuals with dual diagnoses were more likely to be female, have histories of incarceration, and have prior treatment experiences. After 1 year, they had poorer outcomes in terms of employment and drug abstinence, highlighting the need for tailored support in recovery programs.