Background : There are limited data to overcome high post treatment platelet reactivity(HPPR). The purpose of this study was to know the efficacy of high maintenance dose of clopidogrel in patients showing high post clopidogrel P2Y12 reactivity (HPCPR) on usual dose dual antiplatelet therapy. Methods and Results : Impedance platelet aggregometry and point-of-care assay were taken in 40 patients on usual dose dual antiplatelet therapy after coronary drug eluting stent implantation. Two modalities of platelet function test correlated well(r2=0.29, p<0.001). Maintenance dosage of clopidogrel was doubled in 22 patients (55%) showing high post treatment P2Y12 reactivity ( PRU > 239). After one month treatment of high dosage clopidogrel, 9 patients ( 40.9% ) did not show HPCPR. By impedance platelet aggregometry, higher portion of HPCPR patients( 5 of 7 patients, 71.4%) showed improved response of platelet reactivity after high dose clopidogrel treatment. Maintenance of high dose clopidogrel was well tolerated in all patients without any side effects during the study period. Conclusions : Our study suggests that high dose clopidogrel therapy is one of the effective and safe strategies to overcome HPCPR in patients after drug eluting coronary stent implantation. Table : Comparison of platelet reactivity before and after high dose clopidogrel treatment by aggregometry and point-of-care assay