A clinical trial to evaluate the safety and effectiveness of hydroxychloroquine for the treatment of adults hospitalized with COVID-19 has been stopped by the U.S. National Institutes of Health (NIH), the agency announced on Saturday.

A data and safety monitoring board met late Friday and determined that while there was no harm, the study drug was very unlikely to be beneficial to hospitalized patients with COVID-19, according to a release of the NIH.

The data from the Outcomes Related to COVID-19 treated with hydroxychloroquine among In-patients with symptomatic Disease study, or ORCHID Study, indicate that this drug provided no additional benefit compared to placebo control for the treatment of COVID-19 in hospitalized patients.

The first participants enrolled in the trial in April at Vanderbilt University Medical Center, Nashville, Tennessee. The blinded, placebo-controlled randomized clinical trial aimed to enroll more than 500 adults who are currently hospitalized with COVID-19 or in an emergency department with anticipated hospitalization.

More than 470 were enrolled at the time of study's closure, according to the NIH.

ORCHID participants had been randomly assigned to receive hydroxychloroquine 400 mg twice daily for two doses on day one, then 200 mg twice daily for the subsequent eight doses on days two to five, or a placebo twice daily for five days.

The U.S. Food and Drug Administration also revoked the emergency use authorization (EUA) that allowed for chloroquine phosphate and hydroxychloroquine used to treat certain hospitalized patients with COVID-19 earlier this week.

Based on its ongoing analysis of the EUA and emerging scientific data, the FDA determined that chloroquine and hydroxychloroquine are unlikely to be effective in treating COVID-19 for the authorized uses in the EUA.

Additionally, 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, said the FDA.

Hydroxychloroquine is used to treat malaria and rheumatoid conditions such as arthritis.