Data sources and search strategy
This systematic literature review and meta-analysis was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement (supplementary Table S1)7. Two databases, including the Medical Literature Analysis and Retrieval System Online (MEDLINE) and Embase were searched using a comprehensive search strategy to identify eligible studies published in the English language from January 2000 to May, 2020. Search terms used were ” diabetes mellitus”, ” type 2/ or hyperglycemia”, ” noninsulin-dependent diabetes mellitus”, ” T2D”, ” T2DM ” ” type 1 diabetes”, ”type 1 diabetes mellitus”, ”insulin-dependent diabetes mellitus”, ” T1DM”, ” drug therapy”, ” medication”, ” medication adherence”, ” patient compliance”, ” developing countries”, ”low-income”, ”middle-income”, ”low income”, ”middle income”, ”LMIC”, ”developing” underdeveloped”, ”under-developed”, ”emerging”, ”less-developed”, ”least-developed”, ”less-economically developed”, ”least-economically developed”, ”less-affluent”, and ”least-affluent”. Detail tables on the search terms used are provided in the supplementary Table S2. Secondary searches that included screening references of the included studies and the previous systematic review8 resulted in the identification of an additional 12 eligible studies for full-text screening (Figure 1).