In a phone interview from his home, where he has been in self-isolation, Dr. Zelenko, who goes by Zev, described a dizzying week filled with calls from media and health officials from countries including Israel, Ukraine and Russia, all seeking information about his treatment. Some world leaders, including Brazil’s president, Jair Bolsonaro, are also talking up some of the same drugs as a cure.

“It’s a very surreal moment,” said Dr. Zelenko, who has been practicing medicine for 16 years. “I’m a simple country doctor, you know. I don’t have connections.”

The online spread of his treatment plan may have real-world consequences as countries consider testing the drugs he recommends on patients. Their popularity has also spurred shortages of hydroxychloroquine, which is used to treat lupus, rheumatoid arthritis and other chronic diseases.

In New York’s tight-knit Hasidic community, Dr. Zelenko’s sudden fame has caused tensions. Shortly after he posted on YouTube, a group of village officials wrote an open letter pleading with him to stop. They said he had exaggerated the extent of the coronavirus outbreak in Kiryas Joel, using a small sample of his patients to predict that as many as 90 percent of village residents would get the virus.

“Dr. Zelenko’s videos have caused widespread fear that has resulted in the discrimination against members of the Hasidic community throughout the region,” the officials wrote, disputing the figure.

Critics have accused Dr. Zelenko of getting ahead of scientific research. Several small studies, including a controversial French one of 20 coronavirus patients, have found that hydroxychloroquine may be effective against the coronavirus. This week, doctors in China said it had helped to speed the recovery of a small number of patients who were mildly ill from the coronavirus. But other studies have contradicted those findings, or have been inconclusive.

“Anyone who tells you these drugs work, or don’t work, is not basing that view on science,” said David Juurlink, the head of the division of clinical pharmacology at the University of Toronto. “There’s reason to be optimistic, and there’s also reason to be pessimistic.”