Even before the endorsement from Rogan, who recently came down with COVID-19 and treated it with a cocktail of drugs unproven to be effective against the illness, ivermectin had been growing in popularity. In places like Brazil, Bolivia, Peru, and South Africa—along with the U.S.—people were using it to self-medicate against COVID-19.

Google searches for ivermectin are at an all-time high. Searches for ivermectin jumped alongside other at-home remedies like “hydroxychloroquine” at the start of the pandemic in March 2020, but while the Trump-backed hydroxychloroquine fell out of favor, ivermectin maintained its popularity. Prescriptions for ivermectin jumped to more than 88,000 in the week ended Aug. 13, and some pharmacists have even reported shortages of the drug.

But as with many unproven medicines, it can have fatal consequences.

Calls to poison control centers about ivermectin exposures have risen fivefold over the baseline in July, according to CDC researchers who used data from the American Association of Poison Control Centers.

Mississippi’s health department even issued an alert in August saying 70% of recent calls to the state poison control center had come from people who over-ingested ivermectin from livestock supply stores.

Such dangerous effects from self-prescription have prompted Merck, the manufacturer of the drug, to come out and say there was no scientific basis for ivermectin to be used as treatment against COVID-19 and the Food and Drug Administration to caution against ingestion of the medicine, warning that “using the drug ivermectin to treat COVID-19 can be dangerous and even lethal.”

Beyond ivermectin’s potential dangers, the drug also appears to offer little benefit in the fight against COVID. Researchers looking into the efficacy of ivermectin as a COVID-19 treatment had to shut down a large 1,300 patient trial because the drug had been no better than a placebo at preventing hospitalizations. Dr. Edward Mills, a professor at McMaster University who led the study, noted the team would have discontinued it earlier were it not for the level of public interest in ivermectin.

Researchers and physicians are particularly worried by people who are seeking out ivermectin to prevent COVID-19 in lieu of getting a vaccine.

But this has not stopped Rogan, the popular podcast host who has already been in hot water for suggesting young, fit people don’t need to get the COVID-19 vaccine.

After announcing a few canceled tour dates owing to his illness, Rogan gave a shout-out to the medicine, saying “a wonderful, heartfelt thank you to modern medicine for pulling me out of this so quickly and so easily.”

Instagram captioned his post with a short warning: “Some unapproved COVID-19 treatments may cause serious harm.”

Facebook, owner of Instagram, did not respond to requests for comment.