Background : Response variability of clopidogrel is linked to cytochrome P450 3A4 enzyme system(CYP3A4). There are limited data about the effect of cardiac drugs inhibiting CYP3A4 on high post treatment platelet P2Y12 reactivity. Methods and Results : Ninety one patients on usual dose dual antiplatelet therapy after coronary drug eluting stent implantation were enrolled. Impedance platelet aggregometry and point-of-care assay were taken and the results were analyzed between groups with or without CYP3A4 metabolized statins ( atorvastatin, simvastatin) or calcium channel blockers(CCB). Two modalities of platelet function tests correlated well (r=0.39, p=0.001). There were no differences in the rate of high post treatment platelet reactivity (HPPR) regardless of CYP3A4 metabolized drug medication(Table). Conclusion : Our study suggests that potential negative interaction between clopidogrel and CYP3A4 metabolized statins or CCBs might be clinically insignificant. Further studies are still required to fully elucidate the potential clinical impact of coadministration of CYP3A4-metabolized drugs. Table: Comparison of platelet reactivity between groups with ot without CYP3A4 metabolized concomitant cardiac drugs