Study selection and data abstraction
The titles and abstracts of the studies acquired from the electronic databases were examined separately by two reviewers. Subsequently, we selected the eligible studies after the full-text screenings based on the pre-defined inclusion criteria. Conflicts were settled by the conversation between the two reviewers or communication with the relevant authors. The following data of the included studies were abstracted: study characteristics (first author, year of publication, study design), study population, and baseline characteristics (study period, demographic, sample size, age, female ratio, definition of polypharmacy, follow-up period), effectiveness and safety outcomes, confounders, and outcome data (sample size and the number of events between groups, adjusted HRs).