This observational, cross-sectional case-control study evaluates obsessive-compulsive symptoms among adults with substance use disorder compared with a demographically similar control group without substance use disorder. Patients aged 18-50 years attending the addiction management inpatient and outpatient services at Assiut University Hospital, and healthy controls recruited from relatives, friends, and hospital staff, will complete structured clinical interviews, the Yale-Brown Obsessive-Compulsive Scale, and other standardized scales for psychiatric symptoms, cognition, and quality of life. The main objective is to estimate the prevalence and severity of obsessive-compulsive symptoms in substance use disorder and examine their associations with sociodemographic and clinical factors, addiction severity, and quality of life in the recovery stage.