President Donald Trump endorsed a decades-old malaria drug as a possible treatment for coronavirus patients on Thursday. The only problem is that it seems to be incredibly lethal in some dosages. Bloomberg News reports that Chinese researchers in Wuhan waved off doctors from the drug, known as chloroquine, during the height of their outbreak because they found it could kill an adult who took twice the daily recommended amount, or two grams. In China, the drug was initially recommended for infected patients after some good results in clinical trials—but doctors were later warned about the drug’s deadly side-effects and its usage has been rolled back. Trump said chloroquine had been approved and could be given to patients by doctors with a prescription. He said Thursday: “It’s been around for a long time, so we know that if things don’t go as planned it’s not going to kill anybody.” An FDA spokesperson contradicted Trump and said the drug hadn’t been approved for use in COVID-19 patients. However, U.S. doctors can legally prescribe a drug for any illness if they think it’s appropriate.