Simultaneous competition for cytochrome P450 (CYP) 2C19 and CYP3A4 might diminish clopidogrel's antiplatelet effect by impacting its metabolic activation. This pharmacoepidemiologic study investigated whether proton pump inhibitors (PPIs) and CYP3A4-metabolized statins individually and jointly increase thrombotic events by attenuating clopidogrel's effectiveness. From Korean nationwide claims data (2007–2015), we selected 59,233 patients who initiated clopidogrel and statins after coronary stenting and compared thrombotic risks by PPI or CYP3A4-metabolized statin use or both. PPIs were associated with increased thrombotic risks (hazard ratio (HR) 1.27, 95% confidence interval (CI) 1.12–1.45), unlike CYP3A4-metabolized statins (HR 1.03, 95% CI 0.98–1.07). PPIs with high CYP2C19-inhibitory potential were more relevant than those with low potential (HR 1.28, 95% CI 1.02–1.61). Joint effects of PPIs and CYP3A4-metabolized statins were nonsignificant (relative excess risk due to interaction −0.14, 95% CI −0.34 to 0.07). Concurrent PPIs were associated with increased thrombotic risks in patients receiving clopidogrel and statins; CYP3A4-metabolized statins did not exacerbate PPI-associated risks.