The results come from a study called RECOVERY, funded by the U.K. government, that sought to randomly assign large numbers of patients to multiple potential treatments in the country’s National Health Service. The goal was to rapidly get answers as to what worked and what didn’t.

“Today’s preliminary results from the RECOVERY trial are quite clear – hydroxychloroquine does not reduce the risk of death among hospitalized patients with this new disease,” University of Oxford epidemiologist Martin Landray, one of the study’s leaders, said in a statement. “This result should change medical practice worldwide and demonstrates the importance of large, randomized trials to inform decisions about both the efficacy and the safety of treatments.”

A total of 1,542 received hydroxychloroquine, and 3,132 received usual care. After 28 days of treatment, 25.7% of those on hydroxychloroquine and 23.5% of those received usual care had died, meaning those on hydroxychloroquine were 11% more likely to die. That difference was not statistically significant.