Review question / Objective: What are the effects of single antiplatelet therapy with P2Y12 inhibitor monotherapy versus dual antiplatelet therapy after percutaneous coronary intervention for acute coronary syndrome? Condition being studied: Antiplatelet therapy after percutaneous coronary intervention for acute coronary syndrome. Information sources: The databases will be Medical Literature Analysis and Retrieval System Online (MEDLINE), Excerpta Medica Database (Embase), and Cochrane Library. Searches were conducted on July 25, 2022 and will be updated on August 25, 2022. There will be no language or publication period restrictions.