Allopurinol, one of the most commonly used uric acid–lowering agents, can cause serious adverse events. To investigate the risk factors for allopurinol-induced adverse events, the authors enrolled 94 patients who developed allopurinol-induced adverse events and 378 controls who were randomly chosen from 1934 patients who used allopurinol but did not develop any adverse events in this retrospective case control study. Univariate analysis showed that patients who developed allopurinol-induced adverse events had more chronic kidney disease (46% vs 30%, P = .005), more hypertension (42% vs 30%, P = .036), less tumor lysis syndrome (P = .030), higher cholesterol (P = .013), and lower aspartate aminotransferase (P = .002) and alanine aminotransferase levels (P = .033) and more commonly used angiotensin receptor blockers (27% vs 15%, P = .007), colchicines (16% vs 5%, P = .010), or statins (19% vs 8%, P = .002) than those who did not. In multiple logistic regression analysis, the use of colchicines (odds ratio, 3.11; 95% confidence interval, 1.28-7.58; P = .012) and statins (2.10; 1.03-4.25; P = .041) was an independent risk factor predicting adverse events in allopurinol users. In conclusion, patients who use colchicine or statins are at significant risk for developing allopurinol-induced adverse events.