OBJECTIVES: Many studies have shown that the methadone maintenance treatment (MMT) can effectively and safely reduce heroin use. However, most studies only evaluated and compared drug treatment programs, but did not investigate the influence of area of treatment on individual behaviors and treatment outcome. This study, therefore, aimed to evaluate direct effects of area-level characteristics and interactive effects of area-level characteristics and individual characteristics on Methadone maintenance treatment, after considering individual-level characteristics in Taiwan. METHODS: All opioid-dependent persons from 5 hospitals in 2009 who were participating in the outpatient methadone maintenance program for the first time and met eligibility criteria were enrolled into the study. The impact of MMT on self–perceived health status was assessed by the case manager of each hospital. Health status and treatment outcome were investigated at the first outpatient visit and at 3-month follow-ups. Individual level and area level characteristics were also assessed. Multilevel linear models were used to estimate if the differences of quality of life and opioid treatment index before and after the MMT were significant. RESULTS: A total of 330 opioid-dependent patients were recruited in the study. During the follow-up period, 38% of participants completed study (N=127). The mean age of study participants was 35 years. Most of participants were male, single, low education level, unemployed and smoking. Patients under MMT had statistically significant improvements in total quality of life (t=-4.293, p<0.000), opioid treatment index (OTI) (t=8.44, p<0.000), and the satisfaction of quality of life (t=-4.498, p<0.000). Furthermore, our result indicated that the schizophrenic and older patients had significantly poorer results. In addition, area of treatment was also significantly associated with OTI. CONCLUSIONS: MMT improves the quality of life of patients and reduce drug abuse problems. However, actions should be taken to minimize the variations among areas of treatment.