Two recent retractions indicate why multiple studies and careful analysis are often necessary to draw definitive conclusions, even from the most respected journals.

1. NEJM: Retraction: Cardiovascular Disease, Drug Therapy, and Mortality in Covid-19. N Engl J Med. DOI: 10.1056/NEJMoa2007621.  Link to original article: Cardiovascular Disease, Drug Therapy, and Mortality in Covid-19
2. Lancet: Retraction—Hydroxychloroquine or chloroquine with or without a macrolide for treatment of COVID-19: a multinational registry analysis Original study: Hydroxychloroquine or chloroquine with or without a macrolide for treatment of COVID-19: a multinational registry analysis