Abstract Objectives The aim of this pilot study was to assess the degree of platelet inhibition by adjunctive cilostazol to dual antiplatelet therapy (triple antiplatelet therapy) during the loading phase. Background Cilostazol can reduce ischemia-reperfusion injury and inflammation, which may reduce the risk of clinical events following percutaneous coronary intervention. Although adjunctive cilostazol may increase platelet inhibition, additive platelet inhibition and adequate loading dose (LD) of cilostazol have not been evaluated. Methods This was an open-label, 2-way, crossover study that randomized healthy subjects (n = 20) to aspirin 300-mg and clopidogrel 600-mg LD (dual therapy), or adjunctive cilostazol 200-mg LD (at 0 and 6 hours) to dual therapy (triple therapy). Platelet aggregations after the addition of ADP and arachidonic acid (AA) were measured by light transmittance aggregometry (LTA) and multiple electrode aggregometry (MEA). Results Inhibition of platelet aggregation (IPA: 20 關mol/l ADP, final extent) after triple therapy was significantly higher (p < 0.05) than that after dual therapy at 1, 2, 4, 6, 8 and 10 hours (figure A). In regard to IPA with 1.6 mmol/l AA, triple therapy also showed a greater value than dual therapy (p < 0.05) at 1, 2, 4, 8 and 10 hours (figure B). Adjunctive cilostazol re-loading at 6 hours did not increase platelet inhibition significantly, and all subjects suffered from headache and/or tachycardia. Conclusions Adjunctive cilostazol LD of 200 mg enhances ADP- and AA-induced platelet inhibition than aspirin and clopidogrel LD. However, LD over cilostazol of 200 mg may not be applicable due to accompanying side effects. Key Words: platelet ��� loading dose ��� adjunctive cilostazol ��� clopidogrel ��� aspirin