The U.S. Food and Drug Administration on Monday revoked its emergency use authorization (EUA) for chloroquine phosphate and hydroxychloroquine sulfate to be used as treatments for COVID-19. FDA Chief Scientist Denise M. Hinton wrote that the evidence does not reasonably suggest that the drugs are effective, and asserted that their potential benefits don't outweigh their known health risks.

The two drugs are approved for treating malaria, and hydroxychloroquine is also approved for autoimmune conditions such as lupus and rheumatoid arthritis.

The FDA granted the EUA for the drugs on March 28, but said that recent results from a large clinical study demonstrated that hydroxychloroquine showed no benefit for COVID-19 patients, wither in terms of reducing the disease's mortality or in speeding up people's recovery. It said in the press release, "in light of ongoing serious cardiac adverse events and other potential serious side effects, the known and potential benefits of chloroquine and hydroxychloroquine no longer outweigh the known and potential risks for the authorized use."

Coronavirus on a blue background.

Image source: Getty Images.

President Trump has frequently touted the drugs as a treatment for COVID-19, saying that he himself was taking hydroxychloroquine, and multiple pharmaceutical companies ramped up production of the antimalarials -- among them, Bayer (OTC:BAYR.Y), Teva Pharmaceutical (NYSE:TEVA), Mylan (NASDAQ:MYL), and Novartis (NYSE:NVS).

One large study that raised doubt about the drugs was recently published in the respected medical journal The Lancet, but was retracted by its authors after the source of the underlying data they used was called into question. However, another study published in the New England Journal of Medicine earlier this month showed that hydroxychloroquine did nothing to prevent people exposed to the coronavirus from developing COVID-19.