President Trump has boosted the drug chloroquine, which is used to treat malaria, as a potential treatment for COVID-19, the disease caused by coronavirus.

The FDA has not approved it as a treatment for the coronavirus, though doctors in the US have wide latitude to prescribe drugs for diseases they're not approved to treat.

Dr. Anthony Fauci, Trump's top infectious-disease expert, on Friday stressed the need for clinical study of chloroquine's use for COVID-19.

Trump jumped in shortly after and said he was a "big fan" of using chloroquine and that he "comes from a very positive school when it comes to, in particular, one of these drugs."

He did acknowledge the need to "see how it works out."

Fauci repeatedly had to stress the need for clinical testing and the lack of definitive proof for the treatment during the briefing.

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President Donald Trump has repeatedly touted a decades-old malaria drug as a promising coronavirus treatment, undercutting his own top infectious-disease expert.

At press briefings and on Twitter, he's been playing up the promise of chloroquine and a related pill called hydrochloroquine, drugs that treat malaria but have not yet been rigorously tested and approved for treating the coronavirus.

"HYDROXYCHLOROQUINE & AZITHROMYCIN, taken together, have a real chance to be one of the biggest game changers in the history of medicine," Trump said in a series of tweets on Saturday. "Hopefully they will BOTH be put in use IMMEDIATELY. PEOPLE ARE DYING, MOVE FAST," he continued.

Some doctors hope chloroquine could help treat COVID-19

Some doctors hope chloroquine could be an effective treatment for COVID-19, the disease caused by the coronavirus, and its use against the disease is being studied. French doctors are researching the use of hydrochloroquine together with the antibiotic azithromycin, and early reports have been promising, though the study is small. It isn't a randomized controlled trial, the gold standard for medical research.

Doctors in the US can technically prescribe chloroquine as a treatment, since it is approved for treating other ailments, even though it has not yet been approved for this use. Already, increased use of the pills has led to a shortage, making it difficult for patients who rely on the drugs to get refills, such as people with lupus.

At a briefing on Thursday, Trump said chloroquine and hydroxychloroquine had been approved by the Food and Drug Administration to treat the coronavirus. But shortly after, FDA Commissioner Stephen Hahn contradicted Trump, saying that the FDA would need to determine that in a clinical trial. The drug has not been approved for COVID-19 patients.

Fauci clarifies that chloroquine evidence is 'anecdotal'

With confusion about the drugs' efficacy in treating the coronavirus swirling and public demand spiking, reporters asked for clarification at Friday's White House briefing about whether the drugs were known treatments for COVID-19.

Dr. Anthony Fauci, the head of the National Institute of Allergy and Infectious Diseases, responded bluntly: "The answer is no, and the evidence that you're talking about ... is anecdotal evidence.

"We're trying to strike a balance between making something with a potential of an effect to the American people available, at the same time that we do it under the auspices of a protocol that would give us information to determine if it's truly safe and truly effective," Fauci said. "But the information that you're referring to specifically is anecdotal, it was not done in a controlled clinical trial. So you really can't make any definitive statement about it."

Trump continued to promote the drug as he did on Thursday, jumping in immediately after Fauci finished speaking to add that he was a "big fan" of chloroquine.

'I like to prove things first'

Trump acknowledged Fauci's assessment, saying "it's early" but added, "I've seen things that are impressive and we'll see. We're going to know, so we're going to know soon, including safety, but, you know, when you get that safety this has been prescribed for many years for people to combat malaria, which was a big problem, and it's very effective. It's a strong — it's a strong drug, so we'll see."

"I will say that I am a man that comes from a very positive school when it comes to, in particular, one of these drugs, and we'll see how it works out," he said later in the press conference.

After another round of questions about the drugs, Fauci once again returned to the podium, this time striking a more conciliatory tone with the president but still emphasizing the need for clinical testing.

"Fundamentally, I think it probably is going to be safe, but I like to prove things first, so it really is a question of not a lot of difference," Fauci said. "It's the hope that will work, versus proving that it will work."