CYP2C19 and Stroke: The genetic study of the CHANCE subgroup showed that in patients with acute ischemic stroke or transient ischemic attack treated with clopidogrel, those with the CYP2C19 LoFA were more at risk of stroke and composite vascular events than those without, and the presence of CYP2C19 LoFA reduced the efficacy of clopidogrel by 20% [9].