President Donald Trump emphatically defended himself on Tuesday against criticism from medical experts that his announced use of a malaria drug against the coronavirus could spark wide misuse by Americans of the unproven treatment with potentially fatal side effects.

Trump’s revelation a day earlier that he was taking hydroxychloroquine caught many in his administration by surprise and set off an urgent effort by officials to justify his action. But their attempt to address the concerns of health professionals was undercut by the president himself.

He asserted without evidence that a study of veterans raising alarm about the drug was “false” and an “enemy statement,” even as his own government warned that the drug should be administered for Covid-19 only in a hospital or research setting.

“If you look at the one survey, the only bad survey, they were giving it to people that were in very bad shape,” Trump said. That was an apparent reference to a study of hundreds of patients treated by the Department of Veterans Affairs in which more of those in a group who were administered hydroxychloroquine died than among those who weren’t.

“They were very old. Almost dead,” Trump said. “It was a Trump enemy statement.” During a Cabinet meeting, he elicited a defense of his practice from other officials, including VA Secretary Robert Wilkie who noted that the study in question was not conducted by his agency.

But the drug has not been shown to combat the virus in a multitude of other studies as well. Two large observational studies, each involving around 1,400 patients in New York, recently found no Covid-19 benefit from hydroxychloroquine. Two new ones published last week in the medical journal BMJ reached the same conclusion.

No large, rigorous studies have found the drug safe or effective for preventing or treating Covid-19.

Trump said he decided to take hydroxychloroquine after two White House staffers tested positive for the disease, but he already had spent months promoting the drug as a potential cure or preventive despite the cautionary advice of many of his administration’s top medical professionals.

“This is an individual decision to make,” Trump told reporters during a visit to Capitol Hill to meet with Senate Republicans. He later claimed, “It’s gotten a bad reputation only because I’m promoting it.”

Many studies are testing hydroxychloroquine for preventing or limiting coronavirus illness but “at this point in time there’s absolutely no evidence that this strategy works,” said Dr. Carlos del Rio, an infectious-disease specialist at Emory University in Atlanta.

FDA Commissioner Stephen Hahn said in an emailed statement Tuesday: “The decision to take any drug is ultimately a decision between a patient and their doctor.”

As research started to emerge that hydroxychloroquine was not helpful, and even potentially harmful, in battling Covid-19, the president’s public rhetoric in support of the drug had faded. But his private hopes had not, according to three White House officials and Republicans close to the White House not authorized to speak publicly about private discussions.

Trump also lashed out at House Speaker Nancy Pelosi, calling her a “sick woman” who has “a lot of mental problems” after she questioned Trump’s use of the drug because he is 73 and falsely labeled him “morbidly obese.” Her comments were followed by Senate Democratic leader Chuck Schumer, who told MSNBC that Trump’s move was “reckless, reckless, reckless.“

Trump’s presumptive Democratic opponent in the 2020 election, Joe Biden, chastised the president for being irresponsible in taking hydroxychloroquine.

“What is he doing? What in God’s name is he doing?” Biden said during a Yahoo News town hall Tuesday night. “The words of a president matter.”

After two staffers were known to test positive for Covid-19 earlier this month, the White House mandated that those in the West Wing wear face coverings and introduced daily testing for the president, vice president and those they come in close contact with.

Pence told Fox on Tuesday that he was not taking the drug because his doctor did not recommend it, but said he “would never begrudge any American taking the advice of their physician.”

Prescriptions for hydroxychloroquine surged roughly 80 per cent in March to more than 830,000 compared with same period in the prior year, according to data tracking firm IQVIA. That jump in prescribing came before the federal government accepted nearly 30 million doses of the drug donated to the strategic national stockpile by foreign drugmakers. Since then, millions of those tablets have been shipped to US hospitals nationwide for use treating patients with Covid-19.