evidence: "We know that every single good study - and by good study I mean randomised control study in which the data are firm and believable - has shown that hydroxychloroquine is not effective in the treatment of Covid-19," he said. [...] President Trump and his son Donald Trump Jr were among social media users who shared video late on Monday of a group called America's Frontline Doctors advocating hydroxychloroquine as a Covid-19 treatment. [...] Asked about hydroxychloroquine earlier on Tuesday, Dr Fauci said the medication was not an appropriate treatment for Covid-19.