We evaluated the interaction between protease-activated receptor-1 antagonist vorapaxar and concomitant glycoprotein (GP) IIb/IIIa receptor inhibitors in patients with non-ST-segment elevation acute coronary syndromes who underwent PCI. In Thrombin Receptor Antagonist for Clinical Event Reduction in Acute Coronary Syndrome trial, 12,944 patients with non-ST-segment elevation acute coronary syndromes were randomized to vorapaxar or placebo. Administration of GP IIb/IIIa receptor inhibitors was allowed at the treating physician's discretion. We investigated whether use of GP IIb/IIIa receptor inhibitors modified vorapaxar's effect on non-coronary artery bypass grafting (CABG)-related bleeding at 7 days and ischemic events at 30 days. In total, 7,455 patients underwent PCI during index hospitalization. Of these, 2,023 patients (27.1%) received inhibitors and 5,432 (72.9%) did not. Vorapaxar was associated with a numerically higher rate of non-CABG-related moderate/severe Global Use of Strategies to Open Occluded Arteries (GUSTO) bleeding at 7 days compared with placebo in those who did (1.3% vs 1.0%) and did not (0.6% vs 0.4%) receive GP IIb/IIIa receptor inhibitors. Ischemic end point rates at 30 days were not significantly lower with vorapaxar versus placebo. Increased rates of non-CABG GUSTO moderate/severe bleeding were observed in patients who received GP IIb/IIIa receptor inhibitors versus those who did not (adjusted hazard ratio [HR] 1.77, 95% confidence interval [CI] 0.43 to 7.35 in placebo arm; adjusted HR 2.02, 95% CI 0.62 to 6.61 in vorapaxar arm) and in those who received vorapaxar versus placebo (adjusted HR 1.54, 95% CI 0.36 to 6.56 in the GP IIb/IIIa group; adjusted HR 1.34, 95% CI 0.44 to 4.07 in the no-GP IIb/IIIa group). No interaction was found between vorapaxar and inhibitor use up to 7 days (P interaction = 0.89) nor at the end of the treatment (P interaction = 0.74); however, the event rate was low. Also, no interaction was observed for efficacy end points after PCI at 30 days or at the end of the treatment. In conclusion, GP IIb/IIIa receptor inhibitor use plus dual antiplatelet therapy in a population with non-ST-segment elevation myocardial infarction planned for PCI was frequent but did not interact with vorapaxar's efficacy or safety. Nonetheless, GP IIb/IIIa receptor inhibitors and vorapaxar were associated with increased bleeding risk, and their combined use may result in additive effects on bleeding rates.