A genotype-guided P2Y12-inhibitor de-escalation strategy, switching acute coronary syndrome (ACS) patients without a CYP2C19 loss-of-function allele from ticagrelor or prasugrel to clopidogrel, has shown to reduce bleeding risk without affecting the effectivity of therapy by increasing ischaemic risk. This evidence concerns the gene CYP2C19 and acute coronary syndrome.