Background: Mental and physiological responses to the repeated use of drugs are called dependency. Opioid bowel dysfunction (OBD) is common side effect associated with opium. OBD has many manifestations such as abdominal pain, abdominal cramping, bloating and gastroesophageal reflux but is known commonly by constipation. Narcotic bowel syndrome (NBS) is a subset of OBD characterized by recurrent and chronic abdominal pain getting worse by continuing or increasing doses of opium. Due to ever increasing incidence of consumption of narcotics drugs and also expanded spread of gastrointestinal disorders in people of society and due to lack of precise studies in such cases in Iran, research in this field seemed vital.Methods: In this cross-sectional study, among all methadone maintenance therapy (MMT) clinics in Isfahan, Iran, 4 centers were selected by easy non-probability sampling method in 2012 fall. A questionnaire was distributed among the opioid consumers. The questionnaire contained demographic information sucs as age, sex, occupation, and duration of drug use, drug type, duration of MMT, gastrointestinal symptoms and the severity of the symptoms.Findings: From 192 completed and collected questionnaires, 184 were acceptable. The most common gastrointestinal symptoms in patients were constipation, abdominal pain, belching and bad taste in the mouth, respectively. The severity of symptoms and extent of methadone use in patients were assessed and gastrointestinal symptoms were not associated significantly with methadone dose of patients.Conclusion: In this study, the prevalence of gastrointestinal symptoms among patients in addiction clinics was assessed and the most common digestive complaint of these patients was constipation. Severity of constipation and other gastrointestinal symptoms were unrelated with amount of methadone use and the type and amount of prior drug use.