The French government is revoking a decree that had allowed hospitals to prescribe hydroxychloroquine in some COVID-19 cases, saying there is no proof that it helps patients — and citing data that shows it could cause heart problems and other health risks. "This molecule must not be prescribed for patients affected by COVID-19," the Ministry of Solidarity and Health said as it announced the change. The move to bar hospitals from prescribing the drug for coronavirus patients comes two days after the World Health Organization halted clinical trials of hydroxychloroquine as a treatment for COVID-19. The WHO cited a study published in The Lancet, that had found no benefit from the drug and reported a higher mortality rate for hospitalized patients and "an increased frequency of ventricular arrhythmias." France's health ministry had approved hydroxychloroquine for emergency prescriptions in COVID-19 cases in late March. As France 24 reports, that's when French researcher Didier Raoult, who has been an insistent proponent of hydroxychloroquine, said he had successfully treated COVID-19 patients using the controversial drug in combination with azithromycin. But the health ministry says recent studies show the treatment can produce "cardiac toxicity, particularly in combination with azithromycin." Researchers continue to evaluate the possible use of hydroxychloroquine, which is used to treat malaria and lupus, to fight the coronavirus, with at least two studies underway in the U.S. As NPR's Joe Palca reports, the drug has been found to be able to prevent replication of the coronavirus.