OBJECTIVE: Patients with diabetes mellitus (DM) presenting with acute coronary syndrome (ACS) and undergoing percutaneous coronary intervention (PCI) derived enhanced benefit with dual antiplatelet therapy (DAPT) with prasugrel vs. clopidogrel. The risk profile and treatment response to DAPT for medically managed ACS patients with DM remains uncertain. METHODS: The TRILOGY ACS trial compared aspirin + prasugrel vs. aspirin + clopidogrel for up to 30months in non-ST-segment elevation (NSTE) ACS patients managed medically without revascularization. We compared treatment-related outcomes among 3539 patients with DM vs. 5767 patients without DM. The primary endpoint was a composite of cardiovascular death, myocardial infarction, or stroke. RESULTS: Patients with vs. without DM were younger, more commonly female, heavier, and more often had revascularization prior to the index ACS event. The frequency of the primary endpoint through 30months was higher among patients with vs. without DM (24.8% vs. 16.3%), with a higher risk for those patients with DM treated with insulin vs. those treated without insulin (35.3% vs. 19.9%). There was no significant difference in the frequency of the primary endpoint by treatment with prasugrel vs. clopiodgrel in those with or without DM (Pint=0.82) and with or without insulin treatment among those with DM (Pint=0.304). CONCLUSIONS: Among NSTE ACS patients managed medically without revascularization, patients with DM had a higher risk of ischemic events that was amplified among those treated with insulin. There was no differential treatment effect with a more potent DAPT regimen of aspirin + prasugrel vs. aspirin + clopidogrel.