Hydroxychloroquine, once heavily promoted as a COVID-19 treatment by President Donald Trump, did not demonstrate a clinical benefit when prescribed to prevent infection with the virus, according to a small new study published Wednesday in JAMA Internal Medicine. Hydroxychloroquine and chloroquine, a sister formulation, are approved in the U.S. as treatments for malaria, lupus, and rheumatoid arthritis. In the early days of coronavirus outbreaks in the U.S., the Food and Drug Administration granted an emergency use authorization to the drug, which was then tested in multiple clinical trials as a treatment and also for post-exposure and pre-exposure prophylaxis. (The EUA was later revoked.) This randomized, placebo-controlled study evaluated an eight-week regimen of hydroxychloroquine in 132 hospital-based health care workers in Pennsylvania who had been exposed to patients with COVID-19. Giving the workers hydroxychloroquine "did not reduce the incidence of SARS-CoV-2 infection compared with placebo," the researchers wrote. A number of studies published this summer also found that hydroxychloroquine did not benefit COVID-19 patients or work to prevent infection.