Hydroxychloroquine, a drug used to both prevent and treat malaria and some autoimmune diseases, has been praised by US President Donald Trump as a possible "game changer" in combating the novel coronavirus.

US President Donald Trump revealed on Monday's roundtable with restaurant executives that he is taking hydroxychloroquine as a preventive measure against COVID-19, noting that he takes "a pill every day".

"I happen to be taking it. I'm taking it, hydroxychloroquine", Trump said. 

Trump told reporters that he has been taking the drug "for about a week and a half", adding that he takes zinc as a preventative measure. He noted that he has not been infected by the disease and has shown no symptoms from the medication.

In April, the Food and Drug Administration (FDA) warned that using hydroxychloroquine or chloroquine for COVID-19 outside of a hospital setting or a clinical trial could cause heart problems.

When asked about his reasons for choosing this drug, POTUS responded that he thinks "it's good" and noted that he "heard a lot of good stories", and asserted that "a lot of frontline workers and doctors" take it.

Earlier in the week, the US enrolled the first 2,000 coronavirus-positive adults in the second phase of a clinical trial using hydroxychloroquine, to determine whether the drug works against COVID-19. The first phase of the trial confirmed that it is safe, but did not provide evidence that it helps in stopping the disease. 

Hydroxychloroquine is a drug used in malaria and autoimmune disease treatment. It was praised by Trump as a possible "game changer" in the fight against the novel coronavirus, as some epidemiologists believe that the drug can be effective against COVID-19, if combined with zinc and azithromycin.

A study published in the Journal of the American Medical Association on 11 May did not find evidence that hydroxychloroquine would be an effective treatment for COVID-19 patients.