The aim of this study was to investigate the association between CYP2C19 gene polymorphisms and the risk of cardiovascular events in the early stage and subsequent period after percutaneous coronary intervention (PCI) among patients who received clopidogrel. Between October 2015 and January 2017, CYP2C19 genotyped patients who were treated with clopidogrel after PCI were enrolled in this study. Included patients were categorized as non–loss-of-function metabolizers, intermediate metabolizers, and poor metabolizers based on CYP2C19 genotype. The primary outcome was a composite of any-cause mortality, nonfatal myocardial infarction, nonfatal ischemic stroke, and stent thrombosis occurring during exposure to clopidogrel. The rates of clinical outcome events were compared between CYP2C19 phenotypes. Landmark analyses were processed at 90 days and 1 year post-PCI. Of 1341 patients, 161 (12.0%) had 2 copies of loss-of-function (LOF) alleles, 621(46.3%) had one LOF allele, and 559 (41.7%) had no LOF allele. At the 3-month follow-up, the primary outcome events were more frequent in carriers of 2 LOF alleles (5.6%) than in noncarriers (1.8%) [adjusted hazard ratio (HR) 2.944, 95% confidence interval, 1.184–7.321, P = 0.020). A similar finding was observed among in patients with acute coronary syndrome indications at the index PCI (adjusted HR 3.046, 95% confidence interval, 1.237–7.501, P = 0.015). These differences did not persist within the subsequent 9 months of follow-up, among either all comers or subjects with acute coronary syndrome. In conclusion, these data demonstrate a higher risk for ischemic events in patients with 2 CYP2C19 LOF alleles who are prescribed clopidogrel, seen at 3 months after PCI, that is not sustained for 12 months.