Donald Trump has said he is taking an anti-malarial drug to lessen symptoms should he get coronavirus, even though the drug is unproven for fighting Covid-19.
The president told reporters he has been taking hydroxychloroquine and a zinc supplement daily "for about a week and a half now".
Mr Trump spent weeks pushing the drug as a potential cure for Covid-19 against the advice of many of his administration's top medical professionals.
The drug has the potential to cause significant side effects in some patients and has not been shown to combat coronavirus.
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Mr Trump said his doctor did not recommend the drug to him but he requested it from the White House physician.
"I started taking it, because I think it's good," he said.
"I've heard a lot of good stories."
He dismissed reports of side effects, saying: "All I can tell you is, so far I seem to be OK."
Mr Trump has repeatedly pushed the anti-malarial with or without the antibiotic azithromycin, but no large, rigorous studies have found them safe or effective for preventing or treating Covid-19.
They can cause heart rhythm problems and other side effects.
The US's Food and Drug Administration has warned against the drug combo and said hydroxychloroquine should only be used for coronavirus in formal studies.
Two large observational studies, each involving around 1,400 patients in New York, recently found no benefit from hydroxychloroquine.
Two new ones published on Thursday in the medical journal BMJ reached the same conclusion.
One, by French researchers, gave 84 hospital patients the drug and 97 others the usual care.
There were no differences in the odds of death, need for intensive care or developing severe illness.
The other study from China was a stricter test: 150 adults in hospital with mild or moderate illness were randomly assigned to receive hydroxychloroquine or usual care.
The drug made no difference in rates of clearing the virus or time to relief of symptoms, and they brought more side effects.
In April, the National Institutes of Health launched a study testing hydroxychloroquine versus a placebo drug in 500 Covid-19 patients.
Last week, NIH announced another study to see if hydroxychloroquine plus azithromycin can prevent hospital admission or death in people with mild to moderate illness.
About 2,000 US adults with confirmed coronavirus infections and symptoms such as fever, cough or shortness of breath will receive the drugs or placebo pills.
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