NEW YORK (NYTIMES, BLOOMBERG) - US President Donald Trump has said that the federal government is placing millions of doses of a malaria drug in the federal stockpile of emergency medical supplies to make it available for coronavirus patients, even though the drug has not been approved for Covid-19 treatment and his top coronavirus advisers have warned that more study is needed to determine its safety and efficacy.

Though advisers, including Dr Anthony Fauci, have cautioned many times that more data is needed on the drug hydroxychloroquine, Mr Trump, in a White House briefing on Saturday (April 4), went so far as to urge patients to take it.

"What do you have to lose? Take it," the President said. "I really think they should take it. But it's their choice. And it's their doctor's choice or the doctors in the hospital... Try it, if you'd like."

During the briefing, as Dr Fauci and other advisers looked on, the President talked about the potential of other medicines too. He mentioned azithromycin, often referred to as a Z-Pak, which has been given to some patients along with hydroxychloroquine.

"The other thing, if you have a heart condition, I understand, probably you stay away from the Z-Pak. But that's an antibiotic. It can clean out the lung. The lungs are a point of attack for this horrible virus."

In addition to treating malaria, hydroxychloroquine is also prescribed for rheumatoid arthritis, lupus and some other autoimmune diseases. Laboratory studies in cultured cells have suggested that it may block the coronavirus from invading cells.

And some researchers think its ability to dial back an overactive immune system - the reason it is used for autoimmune diseases - might help relieve the life-threatening inflammation that develops in some coronavirus patients.

Still, there is no definitive proof that it works against the coronavirus, and it does not have Food and Drug Administration (FDA) approval for that use. Early reports from China and France suggested that it could help, but the studies had flaws that made the findings less than reliable. Many researchers have called for controlled clinical trials to determine once and for all whether hydroxychloroquine has any value for coronavirus patients.

A more recent study from China was conducted more carefully than the earlier ones, and found that the drug did help, but the study was small, included only mildly ill patients and its authors said more research was needed.

Mr Trump seized on the drug several weeks ago, at one point saying it would be a "game changer" in the course of the pandemic. Hoarding and a run on the drug followed, leaving patients who rely on the drug for chronic diseases wondering whether they would be able to fill their prescriptions.

On Saturday, he continued with that message. "If this drug works, it will be not a game changer because that's not a nice enough term. It will be wonderful," he said. "It will be so beautiful. It will be a gift from heaven if it works."

With no proven treatment for the coronavirus, many hospitals in the United States have simply been giving hydroxychloroquine to patients, reasoning that it might help and probably will not hurt, because it is relatively safe. But it is not considered safe for people with abnormal heart rhythms.

At the Saturday briefing, Dr Stephen Hahn, commissioner of the FDA, said the agency had given special permission for imported hydroxychloroquine to be used in the US, in part to make sure that there would be enough for patients who need it for chronic diseases like lupus.

On Friday, Dr Fauci, the director of the National Institute of Allergy and Infectious diseases, warned Americans against assuming that the drug would be a silver bullet against the coronavirus, noting that evidence of its effectiveness was scant and more studies were needed.

But on Saturday, Mr Trump continued to wax enthusiastic.

"We're going to be distributing it through the Strategic National Stockpile," he said, adding: "We have millions and millions of doses of it; 29 million to be exact."

The Department of Health and Human Services directed questions to the Strategic National Reserve, which did not immediately respond to a request for comment.

Mr Trump said he also had spoken to Prime Minister Narendra Modi of India about procuring millions more doses of hydroxychloroquine from that country.

However, it was reported on Sunday that India has put a total ban on exports of hydroxychloroquine. Exports of the drug and its formulations have been prohibited "without any exceptions" and with immediate effect, India's Directorate-General of Foreign Trade said in an April 4 order on its website.

The trade regulator had last month restricted overseas shipments of the drug, allowing only limited exceptions such as on humanitarian grounds and for meeting prior commitments.

The new ban reflects India's rising concern over the rapid spread of the coronavirus, with incidents of community spread emerging from different parts of the country of 1.3 billion people.

Mr Trump said at the briefing that there was a study indicating that patients with lupus did not contract the coronavirus, implying that perhaps their use of hydroxychloroquine was protecting them.

"They should look at the lupus thing. I don't know what it says, but there's a rumour out there that because it takes care of lupus very effectively as I understand it, and it's a, you know, a drug that's used for lupus. So there's a study out there that says people that have lupus haven't been catching this virus. Maybe it's true, maybe it's not."

It is not clear what study he was referring to. Researchers from China did report that they noticed that their lupus patients had not caught the virus, but the observation was anecdotal, not proof.

At the briefing, Dr Fauci said the observation was worth studying.