There is limited knowledge regarding the most efficacious antiplatelet treatment to reduce subsequent stroke risk for patients with CYP2C19 loss-of-function (LOF) alleles presenting with acute cerebrovascular events. Clopidogrel is an inactive prodrug and requires conversion to an active metabolite through the CYP2C19 enzyme.1 Individuals who carry 2 LOF alleles for the CYP2C19 gene are poor metabolizers of clopidogrel, and clopidogrel may be less effective in these patients.1 CYP2C19 LOF alleles are more common in East Asian populations. At least 1 CYP2C19 LOF allele is present in approximately 24% of non-Hispanic White individuals, 33% of Black individuals, 18% of Hispanic individuals, and 50% of Asian individuals.2 Carriers of these LOF alleles were found to have a higher risk of ischemic stroke compared with noncarriers when treated with clopidogrel.3