Background: Ticagrelor is currently recommended for patients with acute coronary syndrome (ACS). However, recent studies have yielded controversial results. Objective: To compare the clinical outcomes of ticagrelor and clopidogrel in ACS patients.Methods: Three electronic databases were queried until April 1, 2021. Major adverse cardiovascular event (MACE) was the primary efficacy endpoint. The secondary efficacy endpoints included stroke, stent thrombosis (ST), cardiovascular (CV) death,

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... use death, and myocardial infarction (MI). The safety endpoints were (major and minor) bleeding. Odds ratios (ORs) and 95% confidence intervals (CIs) and were calculated to represent the estimated effect sizes.Results: Nine clinical trials and 18 observational studies with 269,935 ACS patients were included. No significant difference was detected in MACE (OR 0.76, 95% CI 0.54-1.06, p = 0.11, I² = 66.74%), but ticagrelor introduced a higher risk of bleeding (1.49, 1.14-1.94, 0.00, 63.97%) and minor bleeding (1.57, 1.08-2.30, 0.02, 59.09%) in clinical trials. The secondary efficacy endpoints differed between clinical trials and observational studies. Subgroup analysis demonstrated that ticagrelor showed better therapeutic effects in patients underwent PCI (0.38, 0.23-0.63, 0.00, 0) than those intended for PCI (1.02, 0.70-1.49, 0.93, 68.99%). Meanwhile ticagrelor showed different therapeutic effects on ACS patients of different ethnicities and from different countries.Conclusion:This meta-analysis demonstrated that ticagrelor is not superior to clopidogrel in MACE but is associated with a higher risk of bleeding in ACS patients. Different PCI strategies, ethnicities, and countries may be the factors that contribute to different therapeutic efficacy of ticagrelor.