A World Health Organisation official has warned against the use of the anti-malarial drug hydroxychloroquine to treat Covid-19, following President Donald Trump's claim on May 19 that he was taking the drug. Dr Michael Ryan, executive director of WHO's Health Emergencies Programme, noted that health authorities – including the US Food and Drug Administration – have issued warnings about the drug's potentially lethal side effects. There is no evidence that hydroxychloroquine is effective for treating Covid-19. Dr Ryan said: "Warnings have been issued by many authorities regarding the potential side effects of the drug, and many countries have limited its use to that of clinical trials, or during clinical trials, or under the supervision of clinicians in a hospital setting. That's specifically for Covid-19 because of a number of potential side effects that have occurred and could occur."