Few possible Covid-19 treatments have been as contentious as the antimalarial drug hydroxychloroquine, and a paper published in the NEJM yesterday gives food for thought. The Brazilian study in question, in 504 mild to moderate Covid-19 patients, found no association backing either hydroxychloroquine monotherapy or an azithromycin combination, versus standard of care, in terms of 15-day clinical improvement on a seven-point ordinal scale. The statistics provided the killer blow, yielding p values of 1.00 for both analyses; this effectively means that any hydroxychloroquine benefit is certainly due to chance. Moreover, the odds ratio suggests that patients were 21% more likely to do better on standard of care than on hydroxychloroquine alone – perhaps because the drug caused additional side effects. The antimalarial’s purported role in treating Covid-19 had been given legs by the controversial physician Professor Didier Raoult, and by US president Donald Trump’s disclosure that he was using it to medicate himself against the coronavirus. A retrospective analysis purporting to back it had been published in the Lancet, but was retracted after the authors admitted that they could not vouch for the veracity of primary data sources. The NEJM paper could be the last straw.