Nicorandil is a vasodilatory drug used to relieve angina symptoms. Several healthcare products regulatory agencies have issued a warning associating the use of nicorandil and gastrointestinal (GI) ulceration. We aimed to evaluate the association between use of nicorandil and GI ulceration/perforation. A population-based cohort study involving 1 million randomly sampled participants in Taiwan's National Health Insurance Research Database was carried out. We estimated the association between use of nicorandil and GI ulceration/perforation by a Cox proportional hazards regression model. A nicorandil-specific propensity score (PS) was also created for adjustment of 75 covariates and matching. 25.8% (183/710) of nicorandil-treated patients developed new GI ulcer events and 1.6% (20/1254) developed new GI perforation events in the three-year follow-up period, as compared to 9.3% (61,281/659,081) and 0.3% (2,488/770,537) in the general population comparator cohort. Patients treated with nicorandil were at significantly increased risk of GI ulcer (PS adjusted hazard ratio 1.43, 95% CI, 1.23 to 1.65, 6848 excess cases per 100,000 person years) or GI perforation (aHR 1.60, 95% CI 1.02-2.51, 315 excess cases per 100,000 person years) compared with the nicorandil unexposed population. Our finding may warn the clinicians to weigh the overall risk-benefit balance of nicorandil treatment in patients.