CYP2C19 and transient ischemic attack: To date, very limited data are available addressing the effect of CYP2C19 gene variants on clopidogrel efficacy in IS or TIA.[10,11] Therefore, to define efficacy and safety in carriers of reduced-function CYP2C19 allele, we aim to perform a systematic review and meta-analysis of the accumulated information of association studies between reduced-function CYP2C19 gene variants and clinical outcomes in patients with stroke or TIA.