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Facing those numbers, and in the absence of any known effective treatments, doctors on the frontlines said they began using hydroxychloroquine and the related chloroquine on patients who are deteriorating based on a few small studies suggesting a possible benefit. Some said they had come under pressure from patients to use the therapies widely touted by Trump and other supporters.

“I may take it,” Trump said on Saturday, referring to hydroxychloroquine, though he has twice tested negative for coronavirus, according to the White House. “We’re just hearing really positive stories, and we’re continuing to collect the data.”

Potential side effects of hydroxychloroquine include vision loss and heart problems. But doctors interviewed by Reuters say they are comfortable prescribing the drug for a short course of several days for coronavirus patients because the risks are relatively low and the therapies are inexpensive and generally available.

However, protocols directing how these drugs should be used vary from one hospital to another, including when to introduce them and whether to combine them with other drugs. In addition, some studies showing promise involve patients who took the therapies for mild or early-stage illness. Many of those people are likely to recover from the virus on their own.

Patients admitted to the hospital in the United States are generally much sicker than the mildly ill cases cited in such studies when they receive therapy. These factors, doctors said, have made it difficult for them to determine whether the drugs are making a difference.