President Trump said on Saturday that the federal government was 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, 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. But hydroxychloroquine. 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.