Joe Grinsteiner is a gregarious online personality who touts the anti-parasitic drug ivermectin. In a recent Facebook video, he produced a tube of veterinary-grade ivermectin paste — the kind made for deworming horses.

He gave the tube a squeeze. Then he licked a slug of the stuff, and gulped.

“Yum,” Mr. Grinsteiner said in the Feb. 25 video, one of a number of ivermectin-related posts he has made that have drawn millions of views on Facebook this year. “Actually, that tastes like dead cancer.”

Ivermectin, a drug proven to treat certain parasitic diseases, exploded in popularity during the pandemic amid false claims that it could treat or prevent Covid-19. Now — despite a persistent message from federal health officials that its medical benefits are limited — interest in ivermectin is rising again, particularly among American conservatives who are seeing it promoted by right-wing influencers.

Mr. Grinsteiner, 54, is a Trump supporter and country music performer who lives in rural Michigan. He has claimed in his videos that ivermectin cured his skin cancer, as well as his wife’s cervical cancer. In a video last month, he said a woman told him her nonverbal autistic child had become verbal after using ivermectin. In a recent phone interview, Mr. Grinsteiner said that he takes a daily dose of ivermectin to maintain his general well-being.

There is no evidence to support people taking ivermectin to treat cancer or autism. Yet Mr. Grinsteiner believes that the medical and political establishments just want to keep average people from discovering the healing powers of a relatively affordable drug.