“We’ve used it a fair bit because it was one of the hopes,” Eric Caumes, head of infectious diseases at the Paris hospital, said on BFM TV. “But we don’t have the impression that there’s spectacular efficacy. It’s even probably not effective.” Caumes said he would have more formal data around the end of the week.

U.S. President Donald Trump touted the medicine as promising to curb the Covid-19 pandemic, fueling optimism and prompting some hospitals to stockpile it, but there’s no conclusive evidence that it works against the new coronavirus.

Hydroxychloroquine showed promising results in one small study in France, but its methodology has been challenged. In another small trial in China, the drug was no more effective than conventional care.