Introduction: Methadone maintenance therapy is a well-known approach to the treatment of drug use disorders and harm reduction. But the main challenge is retention rate in MMT Methods: Through simple random sampling, 155 addicts aged between 18-60 years who referred to drug addiction center of university and underwent MMT were followed for at least one year and up to two and half years. Results: Of the total, 3.9% female, 62% married, 37.4% workers and 27.1% were jobless. 80% had education level of less than diploma, 43.2% abused marijuana, 54.2% abused alcohol and 49.7% were living in rented houses. 60% referred to this center because of economical problems, 15.5% because of legal issues and 67.7% because of family pressure. 31.6% were opium and opium resin addicts, 60% were heroin addicts, 8.4% were crack addicts and 21.9% were IV abusers. 76.8% had at least one high risk behavior. Average dose of methadone was 86.5+35 mg/day. Mean survival time was 80 weeks. Relapse rate was 3.3% in the first month, 13.9% in three months, 23.2% in six months, 31.7% in first year and 41. 7% was a total relapse rate. Survival rate had a direct significant statistical relationship with the age, type of drug and method of use. Conclusion: According to the results of the present study that indicate a survival rate of 68.2% in a year and 58.3% after a year and also considering the results of other studies, we can conclude that MMP could be an effective method in the treatment of opiate drug disorders.