WASHINGTON (AP) — Making himself an example for using a malaria drug against the coronavirus, President Donald Trump sent the White House scrambling Tuesday to defend his decision amid medical concerns the unproven treatment could spark misuse of a medication with potentially fatal side effects.

Trump's announcement a day earlier that he was taking the drug, hydroxychloroquine, caught many in his administration by surprise and set off an urgent effort by officials to justify his action. The president's own government has warned that the drug should be administered for COVID-19 only in a hospital or research setting.

Trump decided to take hydroxychloroquine after two White House staffers tested positive for the coronavirus, 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. The drug has the potential to cause significant side effects in some patients and has not been shown to combat the virus.

Amid concerns from some public health experts that Trump’s example could send many more people to misuse the drug, White House press secretary Kayleigh McEnany said Tuesday that “tens of millions of people around the world have used this drug for other purposes,” including malaria prophylaxis. She emphasized that “any use of hydroxychloroquine has to be in consultation with your doctor. You have to have a prescription. That’s the way it must be done.”

The drug is also prescribed for some lupus and arthritis patients.

Trump said his doctor did not recommend hydroxychloroquine to him, but that he requested it from the White House physician.

"I started taking it, because I think it’s good," Trump said. "I’ve heard a lot of good stories.”

The White House physician, Dr. Sean Conley, said in a statement released through the press office that, after “numerous discussions” with Trump about the evidence for and against using hydroxychloroquine, “we concluded the potential benefit from treatment outweighed the relative risks.”

The Food and Drug Administration warned health professionals last month that the drug should not be used to treat COVID-19 outside of hospital or research settings due to sometimes fatal side effects. Regulators issued the alert, in part, based on increased reports of dangerous side effects called in to U.S. poison control centers.

Calls to centers involving hydroxychloroquine increased last month to 96, compared with 49 in April 2019, according to data from the American Association of Poison Control Centers provided to the AP. It was the second month of elevated reports involving the drug, following 79 calls in March. The problems reported included abnormal heart rhythms, seizures, nausea and vomiting.

Trump dismissed reports of side effects, saying, “All I can tell you is, so far I seem to be OK.”

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."

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.

“My concern is, the president has a big bully pulpit ... maybe people will think there’s some non-public evidence” that the drug works because Trump has chosen to use it, del Rio said. “It creates this conspiracy theory that something works and they’re not telling me about it yet.”

House Speaker Nancy Pelosi told CNN, "He's our president, and I would rather he not be taking something that has not been approved by the scientists, especially in his age group and his, shall we say, weight group ... morbidly obese, they say.”

Trump is 73. At his last full checkup in February 2019 he passed the official threshold for being considered obese, with a body mass index of 30.4. According to the Centers for Disease Control and Prevention, a BMI of 40 or above is considered “severe” obesity, which some also call “morbid” obesity.

Senate Democratic leader Chuck Schumer called Trump's remarks on the drug dangerous.

"Maybe he's really not taking it because the president lies about things characteristically,” Schumer said on MSNBC. “I know him saying he is taking it, whether he is or not, is reckless, reckless, reckless.“

At least two White House staffers tested positive for COVID-19 earlier this month, sparking concerns about the steps taken by the administration to protect the president and sending Vice President Mike Pence and other officials into varying forms of self-isolation.

The White House has since mandated that those in the West Wing wear face coverings and has introduced daily testing for the virus for the president, vice president and those they come in close contact with. Trump says he continues to test negative for the coronavirus.

Trump last underwent an “interim” medical checkup in a November visit to Walter Reed National Military Medical Center that was not noted on his public schedule. His last complete physical took place in February 2019.

Several prominent doctors said they worried that people would infer from Trump’s example that the drug works or is safe.

Dr. Patrice Harris, president of the American Medical Association, said she wouldn’t second-guess Trump’s medical care, but added, “I do want the public to know that the FDA has cautioned against taking this medication” for COVID-19.

“We should all let the science and the evidence guide decisions,” and there isn’t proof yet that the drug helps prevent or treat the disease, she said.

White House officials did not say whether any other administration officials were taking the drug.

Trump said he took hydroxychloroquine with an “original dose” of the antibiotic azithromycin. The president has repeatedly promoted the use of the drug with or without the azithromycin, but no large, rigorous studies have found them safe or effective for preventing or treating COVID-19.

Two large observational studies, each involving around 1,400 patients in New York, recently found no COVID benefit from hydroxychloroquine. Two new ones published Thursday in the medical journal BMJ reached the same conclusion.

Prescriptions for hydroxychloroquine surged roughly 80% 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 U.S. hospitals nationwide for use treating patients with COVID-19.

Marchione reported from Milwaukee. AP Medical Writer Matthew Perrone in Washington contributed to this report.