RESUMEN
BACKGROUND: Starting in 2008, Vietnam's national MMT program expanded quickly, but it is struggling with increasing attrition rates and poor adherence among patients. Several studies have reported on MMT retention and adherence, but no overview has yet been published. The objective of this study is to fill that gap and to review factors associated with retention and adherence in MMT in Vietnam. METHODS: A systematic search was conducted using databases of literature - Pubmed, Cochrane, Scopus, Academic search premiere, and SoINDEX. Peer-reviewed empirical studies with full text in English discussing retention attrition and adherence regarding MMT in Vietnam were selected. The results were synthesized using qualitative methods. RESULTS: Adherence and retention rates varied among the 11 included studies. In general, patients in mountainous provinces had lower adherence and retention rates than those in big cities. Retention rates decreased with the studies' follow-up period and had a downward trend over time. Factors associated with adherence and retention can be classified into three groups: individual, community, and institutional factors. Important individual factors areage, education, awareness of MMT and HIV, and co-occurring disorders and comorbidities. Stigma is the major community risk factor, and methadone daily dose, the distance between home and clinic, and clinic's service hours are the three most important institutional factors. CONCLUSIONS: The literature reviewed identifies important factors associated with MMT adherence and retention in Vietnam. The findings suggest further research exploring both subjective and objective factors and more policies to remove social and structural barriers to enhance treatment outcomes.