In mid-April, a small trial in Brazil was halted after some patients developed irregular heart rates. Then a study this week of 368 Veterans Affairs patients, which has not been peer-reviewed, found that it did not help patients avoid the need for ventilators and that the use of the drug alone was associated with an increased risk of death. And this week, a panel of the government’s own experts at the National Institute of Allergy and Infectious Diseases said there was “insufficient data” to recommend taking it to treat symptoms from the virus.