ABSTRACT Objective Simultaneous occurrence of psychological disorders such as obsessive-compulsive disorder (OCD) has been reported in patients with a history of substance abuse. We evaluated the occurrence and severity of OCD in opium and amphetamine users. Methods In this cross-sectional study, patients with a history of opium use (n = 100) or with a history of amphetamine use (n = 100) were studied. The diagnosis of OCD was based on the Yale-Brown Obsessive Compulsive questionnaire. Results Regarding the prevalence of OCD in the two groups of opium and amphetamine users, 36% and 22% suffered from very mild OCD, 48% and 36% from mild OCD, 13% and 27% from moderate OCD and 3% and 15% from severe OCD. The severity of OCD was independent of gender and marital status in both groups. In amphetamine users’ group, OCD severity was linked to patients’ age and time for drug usage. Conclusion The severity of OCD is much more severe in amphetamine-dependent patients than in opium-dependent patients. In opioid-dependent patients, the severity of OCD is independent of gender, age, marital status, or duration of drug use, but in amphetamine-dependent patients, the severity of disorder is directly related to age and duration of amphetamine use.