Abstract: The n e w e ng l a n d j o u r na l of m e dic i n e Original Article Effect of Hydroxychloroquine in Hospitalized Patients with Covid-19 The RECOVERY Collaborative Group*​​ A BS T R AC T BACKGROUND The members of the writing committee (Peter Horby, F.R.C.P., Marion Mafham, M.D., Louise Linsell, D.Phil., Jennifer L. Bell, M.Sc., Natalie Staplin, Ph.D., Jonathan R. Emberson, Ph.D., Martin Wiselka, Ph.D., Andrew Ustianowski, Ph.D., Einas Elmahi, M.Phil., Benjamin Prudon, F.R.C.P., Tony Whitehouse, F.R.C.A., Timothy Felton, Ph.D., John Williams, M.R.C.P., Jakki Faccenda, M.D., Jonathan Underwood, Ph.D., J. Kenneth Baillie, M.D., Ph.D., Lucy C. Chappell, Ph.D., Saul N. Faust, F.R.C.P.C.H., Thomas Jaki, Ph.D., Katie Jeffery, Ph.D., Wei Shen Lim, F.R.C.P., Alan Montgomery, Ph.D., Kathryn Rowan, Ph.D., Joel Tarning, Ph.D., James A. Watson, D.Phil., Nicholas J. White, F.R.S., Edmund Juszczak, M.Sc., Richard Haynes, D.M., and Martin J. Landray, Ph.D.) assume responsibility for the overall content and integrity of this article. The affiliations of the members of the writing committee are listed in the Appendix. Address reprint requests to Dr. Horby or Dr. Landray at the RECOVERY Central Coordinating Office, Richard Doll Bldg., Old Road Campus, Roosevelt Dr., Oxford OX3 7LF, United Kingdom, or at ­recoverytrial@​­ndph​.­ox​.­ac​.­uk. *A complete list of collaborators in the RECOVERY trial is provided in the Supplementary Appendix, available at NEJM.org. Drs. Horby, Mafham, and Linsell and Prof. Juszczak, Dr. Haynes, and Dr. Landray contributed equally to this article. This article was published on October 8, 2020, at NEJM.org. This is the New England Journal of Medicine version of record, which includes all Journal editing and enhancements. The Author Final Manuscript, which is the author’s version after external peer review and before publication in the Journal, is available under a CC BY license at PMC7556338. Hydroxychloroquine and chloroquine have been proposed as treatments for coronavirus disease 2019 (Covid-19) on the basis of in vitro activity and data from uncontrolled studies and small, randomized trials. METHODS In this randomized, controlled, open-label platform trial comparing a range of possible treatments with usual care in patients hospitalized with Covid-19, we randomly assigned 1561 patients to receive hydroxychloroquine and 3155 to receive usual care. The primary outcome was 28-day mortality. RESULTS The enrollment of patients in the hydroxychloroquine group was closed on June 5, 2020, after an interim analysis determined that there was a lack of efficacy. Death within 28 days occurred in 421 patients (27.0%) in the hydroxychloroquine group and in 790 (25.0%) in the usual-care group (rate ratio, 1.09; 95% confidence interval [CI], 0.97 to 1.23; P = 0.15). Consistent results were seen in all prespecified subgroups of patients. The results suggest that patients in the hydroxychloroquine group were less likely to be discharged from the hospital alive within 28 days than those in the usual-care group (59.6% vs. 62.9%; rate ratio, 0.90; 95% CI, 0.83 to 0.98). Among the patients who were not undergoing mechanical ventilation at baseline, those in the hydroxychloroquine group had a higher frequency of invasive mechanical ventilation or death (30.7% vs. 26.9%; risk ratio, 1.14; 95% CI, 1.03 to 1.27). There was a small numerical excess of cardiac deaths (0.4 percentage points) but no difference in the incidence of new major..