The purpose of this study was to investigate the effects of methadone treatment and buprenorphine treatment on retention in treatment, urine drug testing results, psychiatric status, social adjustment, and quality of life among patients involved in long-term treatment with the cited medications. Two hundred thirteen patients (106 on buprenorphine treatment and 107 on methadone treatment) were enrolled in this open study at the 3rd month of their treatment and followed up until the 12th month; those who left the program before the end of the 3rd month of their treatment were not included in the study sample. The results of this study show statistically significant improvements in opioid use, psychiatric status, and quality of life between the 3rd and 12th months for both medications. This study suggests the long-term efficacy of methadone treatment and buprenorphine treatment on symptoms of opioid addiction and quality of life.