In addition to cost and availability, other factors might also affect acceptability of methadone maintenance therapy, such as concerns about the safety and efficacy of the therapy [45] . Greater retention in treatment has been found to result in greater decreases in drug use, criminal activity, and unemployment [46] . The length of drug treatment has a positive association with better post-treatment outcome [46] . However, limited experience with methadone maintenance therapy (MMT) in China shows a high rate of dropouts. International studies have shown that motivational enhancement therapy or motivational interviewing enhances treatment initiation, retention and outcomes in MMT program [47, 48] , and adding behavioral intervention components into MMT programs increases abstinence and reduces HIV risk behaviors [49] . Policy-oriented operational research is needed in China to better understand how to increase the effectiveness of MMT and other harm reduction interventions in the Chinese context.