AbstractThe CYP2C19 gene plays a detrimental role in the metabolism of clopidogrel. This study aimed to investigate the association between CYP2C19 polymorphisms and the clinical efficacy of clopidogrel therapy in patients who have undergone carotid artery stenting (CAS). CYP2C19 genotype screening was performed on 959 ischemic stroke patients. Of these patients, 241 who had undergone CAS were enrolled in the study. They were all followed up for 1 year after stent surgery, and the primary clinical end-points were ischemic events. The frequencies of the CYP2C19*2 and *3 alleles among the 959 patients were 31.80% and 5.06%, respectively. Regarding the 241 participants who had undergone CAS, multivariate Cox regression analysis showed that the CYP2C19 loss-of-function (LOF) alleles (*2 and *3) were risk factors for post-CAS prognosis. Within 1 year of follow-up, the patients carrying the CYP2C19 LOF alleles were more likely to experience ischemic events than those carrying none. The occurrence of ischemic events did not significantly differ between the *2 and *3 allele carriers. Our results suggest that CYP2C19 LOF alleles (*2 and *3) significantly impact the prognosis of patients on clopidogrel therapy after CAS and that the CYP2C19*2 and CYP2C19*3 alleles have the same effects on prognosis.