Clopidogrel (CLO) is a clinical antiplatelet agent, about which there are major concerns because its antiplatelet efficiency decreases with insufficient metabolic activation, leading to “clopidogrel resistance.” We aimed to determine the antiplatelet effects of W1, a novel molecule composed of 2-O-clopidogrel and aspirin (1:1 ratio), on platelet aggregation ex vivo and thrombus formation in vivo, and its susceptibility to CLO resistance in combination with other therapies in rats. Platelets were prepared, and an arteriovenous shunt thrombosis model was established using Wistar rats to measure platelet aggregation and thrombus formation, respectively. W1 markedly inhibited adenosine 5′-diphosphate (ADP)-induced platelet aggregation and thrombus formation dose dependently (0.3, 1, and 3 mg/kg). W1 (3 mg/kg) acted rapidly at 0.5 hours and lasted for 72 hours. W1 prolonged bleeding and clotting times in mice, confirming its antithrombotic properties. Compared with CLO 10 mg/kg, the positive control, W1 3 mg/kg exerted equivalent effects on the above specifications. In addition, cyclic adenosine monophosphate levels, measured in rat platelets, increased rapidly after prostaglandin E1 (alprostadil) stimulation of the vehicle control (0.5% methyl cellulose suspension) and W1 (3 mg/kg)-treated groups. ADP (50 μm) reduced the control levels more remarkably than W1 did (P < 0.05 in 3 minutes or P < 0.001 at 5 minutes), suggesting that W1 suppressed ADP-induced cyclic adenosine monophosphate reduction. This was associated with a significant platelet reactivity inhibition measured using the vasodilator-stimulated phosphoprotein assay. CLO or W1 coadministration with or without omeprazole and amlodipine to rats to investigate the pharmacodynamic interactions revealed that W1 exhibited more stable and potent antithrombotic effects than CLO did. In conclusion, both W1 and CLO showed antiplatelet and antithrombotic effects, while the former exhibited less CLO resistance in combination with omeprazole or amlodipine, 2 drugs that inhibit CLO metabolism. Therefore, this study implies that W1 may be a promising oral antiplatelet agent for reducing CLO resistance after percutaneous coronary intervention.