Background: Aspirin is the only antiplatelet agent with a Class I recommendation for long-term prevention of cardiovascular events in patients with coronary artery disease (CAD). There is inconsistent evidence on how it compares with alternative antiplatelet agents., Objectives: This study compared P2Y 12 inhibitor monotherapy vs aspirin in patients with CAD., Methods: We conducted a patient-level meta-analysis of randomized trials comparing P2Y 12 inhibitor monotherapy vs aspirin monotherapy for the prevention of cardiovascular events in patients with established CAD. The primary outcome was the composite of cardiovascular death, myocardial infarction, and stroke. Prespecified key secondary outcomes were major bleeding and net adverse clinical events (the composite of the primary outcome and major bleeding). Data were pooled in a 1-step meta-analysis., Results: Patient-level data were obtained from 7 trials. Overall, 24,325 participants were available for analysis, including 12,178 patients assigned to receive P2Y 12 inhibitor monotherapy (clopidogrel in 7,545 [62.0%], ticagrelor in 4,633 [38.0%]) and 12,147 assigned to receive aspirin. Risk of the primary outcome was lower with P2Y 12 inhibitor monotherapy compared with aspirin over 2 years (HR: 0.88; 95% CI: 0.79-0.97; P = 0.012), mainly owing to less myocardial infarction (HR: 0.77; 95% CI: 0.66-0.90; P < 0.001). Major bleeding was similar (HR: 0.87; 95% CI: 0.70-1.09; P = 0.23) and net adverse clinical events were lower (HR: 0.89; 95% CI: 0.81-0.98; P = 0.020) with P2Y 12 inhibitors. The treatment effect was consistent across prespecified subgroups and types of P2Y 12 inhibitors., Conclusions: Given its superior efficacy and similar overall safety, P2Y 12 inhibitor monotherapy might be preferred over aspirin monotherapy for long-term secondary prevention in patients with established CAD. (P2Y 12 Inhibitor or Aspirin Monotherapy as Secondary Prevention in Patients With Coronary Artery Disease: An Individual Patient Data Meta-Analysis of Randomized Trials [PANTHER collaborative initiative]; CRD42021290774)., Competing Interests: Funding Support and Author Disclosures This study was funded by institutional support of the Cardiocentro Ticino Institute, Ente Ospedaliero Cantonale, and the Department of Cardiology at Bern University Hospital, which had no role in the data analysis, interpretation, or writing of the report. There was no industry involvement in the design, analysis, or funding of this study. Dr Valgimigli has received personal fees from AstraZeneca; has received grants and personal fees from Terumo; and has received personal fees from Alvimedica/CID, Abbott Vascular, Daiichi-Sankyo, Bayer, CoreFLOW, Idorsia Pharmaceuticals Ltd, Departement Klinische Forschung of Universität Basel, Bristol Myers Squibb SA, Medscape, Biotronik, and Novartis, outside the submitted work. Dr Windecker has received research and educational grants to the institution from Abbott, Abiomed, Amgen, AstraZeneca, Bayer, Biotronik, Boehringer Ingelheim, Boston Scientific, Bristol Myers Squibb, Cardinal Health, CardioValve, Corflow Therapeutics, CSL Behring, Daiichi-Sankyo, Edwards Lifesciences, Guerbet, Infraredx, Janssen-Cilag, Johnson & Johnson, Medicure, Medtronic, Merck Sharp & Dohme, Miracor Medical, Novartis, Novo Nordisk, Organon, OrPha Swiss, Pfizer, Polares, Regeneron, Sanofi, Servier, Sinomed, Terumo, Vifor, and V-Wave; serves as an unpaid advisory board member and/or unpaid member of the steering/executive group of trials funded by Abbott, Abiomed, Amgen, AstraZeneca, Bayer, Boston Scientific, Biotronik, Bristol Myers Squibb, Edwards Lifesciences, Janssen, MedAlliance, Medtronic, Novartis, Polares, Recardio, Sinomed, Terumo, V-Wave, and Xeltis but has not received personal payments by pharmaceutical companies or device manufacturers; is a member of the steering/executive committee group of several investigator-initiated trials that receive funding by industry without impact on his personal remuneration; is an unpaid member of the Pfizer Research Award selection committee in Switzerland and of the Women as One Awards Committee; is a member of the Clinical Study Group of the Deutsches Zentrum für Herz Kreislauf-Forschung and of the Advisory Board of the Australian Victorian Heart Institute; and is chairperson of the ESC Congress Program Committee and Deputy Editor of JACC: Cardiovascular Interventions. Dr Mehran has served on the scientific advisory boards of the American Medical Association, the American College of Cardiology (Board of Trustees Member), the Society for Cardiovascular Angiography & Interventions (Women in Innovations Committee Member), JAMA Cardiology (Associate Editor), and the Cardiovascular Research Foundation (Faculty) (no fee). Dr Woodward is a consultant for Freeline; and has recently been a consultant to Amgen. Dr Schunkert has received personal fees from Amgen, AstraZeneca, Bayer Vital GmbH, Boehringer Ingelheim, Bristol Myers Squibb, Daiichi-Sankyo, Merck Sharp & Dohme, Novartis, Sanofi, Servier, and SYNLAB. Dr Franzone has received payment or honoraria for lectures, presentations, Speaker Bureaus, manuscript writing, or educational events from Edwards Lifesciences and Boehringer Ingelheim. Dr Bhatt discloses the following relationships—advisory board: AngioWave, Bayer, Boehringer Ingelheim, Cardax, CellProthera, Cereno Scientific, Elsevier Practice Update Cardiology, High Enroll, Janssen, Level Ex, McKinsey, Medscape Cardiology, Merck, MyoKardia, NirvaMed, Novo Nordisk, PhaseBio, PLx Pharma, Regado Biosciences, and Stasys; board of directors: AngioWave (stock options), Boston VA Research Institute, Bristol Myers Squibb (stock), DRS.LINQ (stock options), High Enroll (stock), Society of Cardiovascular Patient Care, and TobeSoft; Chair: Inaugural Chair, American Heart Association Quality Oversight Committee; consultant: Broadview Ventures; data monitoring committees: Acesion Pharma, Assistance Publique-Hôpitaux de Paris, Baim Institute for Clinical Research (formerly Harvard Clinical Research Institute, for the PORTICO trial, funded by St. Jude Medical, now Abbott), Boston Scientific (Chair, PEITHO trial), Cleveland Clinic (including for the ExCEED trial, funded by Edwards), Contego Medical (Chair, PERFORMANCE 2), Duke Clinical Research Institute, Mayo Clinic, Mount Sinai School of Medicine (for the ENVISAGE trial, funded by Daiichi Sankyo; for the ABILITY-DM trial, funded by Concept Medical), Novartis, Population Health Research Institute; Rutgers University (for the National Institutes of Health–funded MINT Trial); Honoraria: American College of Cardiology (Senior Associate Editor, Clinical Trials and News, ACC.org; Chair, ACC Accreditation Oversight Committee), Arnold and Porter law firm (work related to Sanofi/Bristol Myers Squibb clopidogrel litigation), Baim Institute for Clinical Research (formerly Harvard Clinical Research Institute; RE-DUAL PCI clinical trial steering committee funded by Boehringer Ingelheim; AEGIS-II executive committee funded by CSL Behring), Belvoir Publications (Editor-in-Chief, Harvard Heart Letter), Canadian Medical and Surgical Knowledge Translation Research Group (clinical trial steering committees), Cowen and Company, Duke Clinical Research Institute (clinical trial steering committees, including for the PRONOUNCE trial, funded by Ferring Pharmaceuticals), HMP Global (Editor-in-Chief, Journal of Invasive Cardiology), Journal of the American College of Cardiology (Guest Editor; Associate Editor), K2P (Co-Chair, interdisciplinary curriculum), Level Ex, Medtelligence/ReachMD (CME steering committees), MJH Life Sciences, Oakstone CME (Course Director, Comprehensive Review of Interventional Cardiology), Piper Sandler, Population Health Research Institute (for the COMPASS operations committee, publications committee, steering committee, and USA national co-leader, funded by Bayer), Slack Publications (Chief Medical Editor, Cardiology Today’s Intervention), Society of Cardiovascular Patient Care (Secretary/Treasurer), WebMD (CME steering committees), Wiley (steering committee); other: Clinical Cardiology (Deputy Editor), NCDR-ACTION Registry Steering Committee (Chair), and VA CART Research and Publications Committee (Chair); patent: Sotagliflozin (named on a patent for sotagliflozin assigned to Brigham and Women's Hospital who assigned to Lexicon; neither Dr Bhatt nor Brigham and Women’s Hospital receive any income from this patent); research funding: Abbott, Acesion Pharma, Afimmune, Aker Biomarine, Amarin, Amgen, AstraZeneca, Bayer, Beren, Boehringer Ingelheim, Boston Scientific, Bristol Myers Squibb, Cardax, CellProthera, Cereno Scientific, Chiesi, CinCor, CSL Behring, Eisai, Ethicon, Faraday Pharmaceuticals, Ferring Pharmaceuticals, Forest Laboratories, Fractyl, Garmin, HLS Therapeutics, Idorsia, Ironwood, Ischemix, Janssen, Javelin, Lexicon, Lilly, Medtronic, Merck, Moderna, MyoKardia, NirvaMed, Novartis, Novo Nordisk, Owkin, Pfizer, PhaseBio, PLx Pharma, Recardio, Regeneron, Reid Hoffman Foundation, Roche, Sanofi, Stasys, Synaptic, The Medicines Company, Youngene, and 89Bio; royalties: Elsevier (Editor, Braunwald’s Heart Disease); site co-investigator: Abbott, Biotronik, Boston Scientific, CSI, Endotronix, St. Jude Medical (now Abbott), Philips, SpectraWAVE, Svelte, and Vascular Solutions; trustee: American College of Cardiology; and unfunded research: FlowCo and Takeda. Dr Steg has received grants, personal fees, and nonfinancial support from Sanofi; has received grants and personal fees from Amarin, Servier, and Bayer; has received personal fees from Amgen, AstraZeneca, BMS, Boehringer Ingelheim, Idorsia, Pfizer, and Novartis; and has a patent on the use of alirocumab to reduce risk after acute coronary syndrome (royalties to Sanofi) pending. Dr Szarek has served as a consultant or on advisory boards (or both) for CiVi, Resverlogix, Baxter, Esperion, Sanofi, and Regeneron Pharmaceuticals, Inc. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2023 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)