Loss-of-function alleles in CYP2C19 are common and can occur in about 15%–20% in White and up to about 40%–60% in Asian inidviduals.67,68 A randomized double-blind placebo-controlled trial included 6412 patients with acute minor stroke or TIA who with rapid point-of care genotyping had been found to be carriers of CYP2C19 loss-of-function alleles.67 The patients were randomized to treatment with either clopidogrel or ticagrelor and both groups in addition received aspirin for the first 21 days after their index event. Here, CYP2C19 is linked to transient ischemic attack.