ResultsĀ 
The flow chart of literature retrieval is presented in Figure 1 . Through searching the PubMed, Embase databases, and prior reviews, our initial search yielded 206 articles, from which a total of 42 duplicate articles were removed. After screening the records, we excluded 77 certain articles such as reviews. By reviewing the title and abstract, 19 remaining studies were potentially available, and further assessed under the full-text screenings. According to the pre-defined inclusion and exclusion criteria, we subsequently excluded 7 studies because (1) article is a meta-analysis (n=1)[16]; (2) studies did not report the relevant outcomes (n=3)[17-19]; (3) studies did not report the classification of polypharmacy (n=3) [20-22]. Finally, a total of 12 studies were included in our meta-analysis[8-10, 15, 23-30].