Substance Use Disorder Among Patients with Primary Mental Illnesses in Southwestern Uganda.

: Substance use is common among people with primary mental illness especially schizophrenia and bipolar disorder compared to the general population and complicates treatment outcomes. We enrolled 385 patients with primary mental illnesses in southwestern Uganda between June and August 2022. We collected information on alcohol and cannabis use, social support, religiosity, adherence to treatment and sociodemographic characteristics. We run a logistic regression model to determine the factors associated with substance use disorder. At multivariable analysis, being male (AOR = 13.61, 95% CI [3.66-50.63]: .001) and prior history of cannabis/alcohol use (AOR = 34.95, 95% CI [8.80-138.72]: .001) were significantly associated with substance use disorder while adherence to treatment was against substance use disorder (AOR = 0.27, 95% CI [0.09-0.83]: .03). Adherence to treatment is protective against substance use disorder among people with mental illness. Interventions aiming at preventing substance use disorder among people with mental illness should aim at promoting adherence to treatment.