The Food and Drug Administration said Monday that it was revoking emergency authorization of two malaria drugs to treat Covid-19, saying that they are “unlikely to be effective.”

The drugs, hydroxychloroquine and a related drug, chloroquine, were heavily promoted by President Trump after a handful of small, poorly controlled studies showed that they could work in treating the disease.

Mr. Trump even took hydroxychloroquine after he was exposed to two people who had tested positive for the coronavirus. The agency said that after reviewing some data, it had determined that the drugs, particularly hydroxychloroquine, did not demonstrate benefits that outweighed their risks.