The medicine hydroxychloroquine, popularised by former US president Donald Trump, does not decrease deaths from Covid-19, probably does not reduce the number of people needing mechanical ventilation, and does not prevent Covid-19. The authors of a Cochrane review published in February 2021 recommended that no new trials of hydroxychloroquine or chloroquine for treating Covid-19 should be started. Cochrane is a highly respected non-profit organisation. It publishes high-quality reviews that evaluate medical interventions. Many doctors consider conclusions of Cochrane review to be definitive. What’s also interesting about this particular review, is that Cochrane reviews frequently end by calling for more research. This one, presumably because of the large number of trials conducted and the large number of side-effects reported, says the opposite: no more trials.