Statistical analysis
We estimated intervention effects by calculating risk ratios (RR) for dichotomous outcomes or mean difference (MD) for continuous outcomes, with a 95% confidence interval (CI). Heterogeneity between studies was calculated using the I2 statistic in Review Manager version 5.4.1. The data were considered substantial heterogeneity if was 50% or greater. When clinical and methodology heterogeneity were considered, subgroup analyses were conducted by the indications (pain or fever relief), the doses of treatment, the different types of AEs, and different dosing times, otherwise meta-analysis was performed using the random-effects model (20). All tests were 2-tailed and p-values < 0.05 was considered statistically significant. Descriptive analyses were conducted if there were insufficient similarity information to pool data. Sensitivity analysis and funnel plots (if more than 10 studies were included (21)) were performed to assess the possible bias.