IntroductionCompulsory treatment has decades of history in Iran; both before and after the Islamic Revolution, but there are many debates regarding its efficacy and effectiveness. Retention Rate is one of the best indices to estimate the efficacy of treatment. This study will compare Retention Rate among people referred from compulsory treatment centers and volunteer participants.MethodsThis was a retrospective (historical) cohort study that has been conducted among people who were taking methadone maintenance treatment (MMT). The study sample was selected from the MMT centers that admit both referral patients from compulsory centers and voluntary patients. All newly admitted patients from March 2017 to March 2018 were enrolled and followed up until March 2019.ResultsA total of 105 participants were recruited for the study. All were males with a mean age of 36.6 ± 7.9 years. Fifty-six percent of individuals were referred from compulsory residential centers. The total one-year retention rate of participants in this study was 15.84%. The one-year retention rate for the patients referred from compulsory residential centers and the non-referred patients was 12.28 and 20.45%, respectively (value ofp= 0.128). Among the other studied factors, only marital status was significantly associated with MMT retention (p= 0.023).ConclusionAlthough the average treatment adherence time for non-referred patients was about 60 days higher than those referred from compulsory residential centers, this study found no significant differences in retention days and a one-year retention rate. Further studies with larger sample sizes and longer follow-ups are needed to explore the efficacy of compulsory treatment methods in Iran.