OBJECTIVES: The causes of drug-induced gastroduodenal injuries primarily include antithrombotic drugs, including low-dose aspirin, non-steroidal anti-inflammatory drugs, and corticosteroids. These drugs are suspected to affect gastric ulcer healing after endoscopic submucosal dissection (ESD). This study aimed to investigate the effects of these drugs on post-ESD ulcer healing. METHODS: This study included 170 lesions (149 patients) who had undergone ESD for early gastric cancer. Post-ESD ulcers were endoscopically measured on the 1st, 28th, and 56th days after ESD and were analyzed to identify potential risk factors for delayed ulcer healing among patients taking antiplatelet drugs, anticoagulant drugs, non-steroidal anti-inflammatory drugs, corticosteroids, and no drugs. RESULTS: Multivariate analysis for the frequency of scarring on the 56 CONCLUSIONS: As antiplatelet drugs, particularly clopidogrel, may delay gastric ulcer healing after ESD, careful endoscopic follow-up and drug therapy are suggested for patients taking these drugs.