Those who advocate a more cautious approach warn that the drug, most commonly used to treat malaria and some autoimmune diseases, has yet to demonstrate its efficacy in treating Covid-19 and can have serious, and sometimes fatal, side effects, especially in people who have heart conditions.

In YouTube videos and on Twitter, Dr. Raoult has argued that physicians and governments should use hydroxychloroquine widely now, and not wait for serious clinical trials. His weekly YouTube updates usually get more than one million views and he has hundreds of thousands of followers on Twitter.

“Some people have gone crazy with methodology,” he said in a video message this week. “Our objective as doctors is to make people better.”

Jean-Paul Stahl, a French doctor of infectious diseases, said his phone was ringing off the hook with patients asking to receive Dr. Raoult’s treatment after seeing his posts on social media. “We have to say no,” Dr. Stahl said. “It’s a matter of patient safety.”