Objective: Managing antithrombotic therapy in patients with atrial fibrillation (AF) and an acute coronary syndrome (ACS) and/or percutaneous coronary intervention (PCI) is challenging and can be affected by prior oral anticoagulant (OAC) treatment. We examined the relationship between prior OAC use and outcomes in the AUGUSTUS trial., Methods: This prespecified secondary analysis is from AUGUSTUS, an open-label, 2-by-2 factorial, RCT to evaluate the safety of apixaban versus vitamin K antagonist (VKA) and aspirin versus placebo in patients with AF and ACS and/or PCI. The primary endpoint, major or clinically relevant non-major bleeding and clinical outcomes were compared in patients receiving (n=2262) or not receiving (n=2352) an OAC prior to enrolment., Results: Patients with prior OAC use had more comorbidities, higher CHA 2 DS 2 -VASC and HAS-BLED scores, and were more likely enrolled following elective PCI. There was no difference in major or clinically relevant non-major bleeding with or without prior OAC (30 days: 5.1% vs 5.9% (adjusted HR (aHR) 0.82, 95% CI 0.63 to 1.06); 180 days: 13.5% vs 13.5% (aHR 0.98, 95% CI 0.83 to 1.16)). Patients with prior OAC use had a lower risk of death or ischaemic events (30 days: 1.7% vs 2.8% (aHR 0.61, 95% CI 0.41 to 0.92); 180 days: 5.4% vs 7.6% (aHR 0.70, 95% CI 0.55 to 0.88)). No interactions between randomised treatment (apixaban vs VKA, aspirin vs placebo) and prior OAC status were observed for outcomes, apart from apixaban (vs VKA) being associated with a lower risk of myocardial infarction with prior OAC use (180 days: 2.0% vs 3.7% (aHR 0.56, 95% CI 0.33 to 0.91()., Conclusions: In AUGUSTUS, prior OAC use was associated with fewer ischaemic events but not more bleeding. In patients with AF and ACS and/or undergoing PCI, clinicians can be assured that the trial results can be applied to patients regardless of their prior OAC status., Trial Registration Number: NCT02415400., Competing Interests: Competing interests: RW: Research grant support (eg, steering committee or data and safety monitoring committee) and/or speaker/consulting honoraria (eg, advisory boards) from: AstraZeneca, Bayer, Boehringer Ingelheim, Bristol Myers Squibb/Pfizer, HLS Therapeutics, and Pfizer. PD: reports no conflicts of interest. RL: Institutional research grants and consulting fees from Bristol Myers Squibb, Pfizer, GlaxoSmithKline, Medtronic PLC, and Sanofi; and consulting fees from Amgen, Bayer, and Boehringer Ingelheim. Wojdyla: Nothing to report. RA: Employee of Bristol Myers Squibb. CBG: Research grants from Bayer, Boehringer Ingelheim, Bristol Myers Squibb, Daiichi Sankyo, Janssen, Pfizer, Armetheon, AstraZeneca, US Food & Drug Administration, GlaxoSmithKline, The Medicines Company, Medtronic Foundation, Medtronic, and Novartis; consulting fees from Bayer, Boehringer Ingelheim, Boston Scientific, Bristol Myers Squibb, Daiichi Sankyo, Janssen, Pfizer, Abbvie, Armetheon, Astra Zeneca, Eli Lilly, Gilead, GlaxoSmithKline, Hoffmann-La Roche, The Medicines Company, National Institutes of Health, Novartis, Sirtex, Verseon, Apple, Medscape, Merck, Novo Nordisk, Roche Diagnostics, and Rho Pharmaceuticals. SW: Research and educational grants to the institution from Abbott, Amgen, BMS, Bayer, Boston Scientific, Biotronik, Cardinal Health, CardioValve, CSL Behring, Daiichi Sankyo, Edwards Lifesciences, Johnson&Johnson, Medtronic, Querbet, Polares, Sanofi, Terumo, Sinomed. SW serves as unpaid advisory board member and/or unpaid member of the steering/executive group of trials funded by Abbott, Abiomed, Amgen, Astra Zeneca, BMS, Boston Scientific, Biotronik, Cardiovalve, Edwards Lifesciences, MedAlliance, Medtronic, Novartis, Polares, Sinomed, V-Wave and Xeltis, but has not received personal payments by pharmaceutical companies or device manufacturers. He is also member of the steering/executive committee group of several investigated-initiated trials that receive funding by industry without impact on his personal remuneration. SW is an unpaid member of the Pfizer Research Award selection committee in Switzerland. ANV: Consulting for Medtronic. DV: Research grants from BMS/Pfizer, Boehringer Ingelheim, Bayer, and Daiichi Sankyo; personal fees from Boehringer Ingelheim, Bayer, and Daiichi Sankyo. Halvorsen: Speaker fees from Bayer, Amgen, AstraZeneca, Boehringer Ingelheim, Bristol Myers Squibb, Pfizer, Sanofi, and Merck. AP: Research grants and consulting/speaker fees from Bayer, AstraZeneca, Sanofi-Aventis, NovoNordisk; research grants from Pfizer, Bristol Myers Squibb, Amgen, CSL Behring. Bahit: Lecture fees from Bristol Myers Squibb, Pfizer; consulting fees from Merck Sharp & Dohme, and CSL Behring. RM: Institutional research grants from AstraZeneca, Bayer, Beth Israel Deaconess, Bristol Myers Squibb/Sanofi, CSL Behring, Eli Lilly/Daiichi Sankyo, Medtronic, Novartis, and OrbusNeich; consulting fees from Boston Scientific, Abbott Vascular, Medscape, Siemens Medical Solutions, Roivant Sciences, and Sanofi; consulting (no fees) from Regeneron Pharmaceuticals; institutional consulting fees from Abbott Vascular, Spectranetics/Phillips/Volcano Corporation, Bristol Myers Squibb, Novartis, and Watermark Research; executive committee member for Janssen Pharmaceuticals and Bristol Myers Squibb; has <1% equity in Claret Medical and Elixir Medical. AP: Institutional research grants and consulting fees/honoraria from Bristol Myers Squibb and CSL Behring; institutional research grants from AstraZeneca, CryoLife, US Food and Drug Administration, National Institutes of Health, Sanofi, VoluMetrix, and Boehringer Ingelheim; and consulting fees/honoraria from Pfizer, AbbVie Pharmaceuticals, NovoNordisk, Portola Pharmaceuticals, Quantum Genetics, Teikoku Pharmaceuticals, VA Cooperative Studies Program, and Zafgen. SG: Research grant support (eg, steering committee or data and safety monitoring committee) and/or speaker/consulting honoraria (eg, advisory boards) from: Amgen, AstraZeneca, Bayer, Boehringer Ingelheim, Bristol Myers Squibb, CSL Behring, Daiichi-Sankyo/American Regent, Eli Lilly, Esperion, Ferring Pharmaceuticals, GlaxoSmithKline, HLS Therapeutics, Janssen/Johnson & Johnson, Merck, Novartis, Novo Nordisk A/C, Pendopharm, Pfizer, Regeneron, Sanofi, Servier; and salary support/honoraria from the Heart and Stroke Foundation of Ontario/University of Toronto (Polo) Chair, Canadian Heart Research Centre and MD Primer, Canadian VIGOUR Centre, Duke Clinical Research Institute, New York University Clinical Coordinating Centre and PERFUSE Research Institute., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)