The goal of this study was to evaluate the efficacy of 1-, 3-, and 8-mg per day doses of buprenorphine in the maintenance treatment of opium-dependent patients over a 6-month treatment period. Participants were 513 opium-dependent individuals who were seeking treatment in an urban outpatient clinic, offering a 1-hr weekly individual counseling session. Overall, 305 patients (59.5%) completed the 6-month study. Completion rates by dosage group were 33.9% for the 1-mg dose group, 64.3% for the 3-mg dose group, and 80.1% for the 8-mg dose group—each significantly different from the other two groups. The results support the efficacy and safety of buprenorphine for outpatient treatment of opium dependence and seem to indicate that the highest dose (8 mg) of buprenorphine was the best of the three doses for Iranian opium-dependent patients to increase their retention in treatment.