Ivermectin began as a Nobel Prize-winning cure for animals before being studied in people with parasite diseases.

Sometime before or after his vitamin drip, Joe Rogan, the celebrity podcaster, ingested ivermectin as part of his “throw the kitchen sink at it” approach to self-treating COVID-19.

Ivermectin has revolutionized the treatment of parasitic infections in humans, including “river blindness,” a tropical disease spread by tiny worms carried by black flies that attacks the cornea. In veterinary medicine, it’s also an efficient horse and cattle dewormer.

But ivermectin for preventing or treating COVID-19, especially in quantities intended for animals?

The health agencies in the US have been warning people, not to take human or veterinary grade versions of ivermectin to curb SARS-CoV-2. Any pills, pastes, oral, injectable or topical solutions purchased for such a purpose, the agency said, should be immediately discarded.

Below, what’s known about ivermectin, and why it is not the miracle cure some would have you believe.

What is it?

“Ivermectin is a wonderful drug,” Joe Schwarcz, director of the McGill Office for Science and Society said this week on one of his regular YouTube videos.

In 2015, Japanese microbiologist Satoshi Omura and Irish-born American biologist and parasitologist William C. Campbell received a half-share of the Nobel Prize in Physiology or Medicine for their discovery of a bioactive agent that proved surprisingly effective against parasites in domestic and farm animals.

“Ivermectin was later tested in humans with parasitic infections and effectively killed parasite larvae,” the Nobel Assembly noted in a press release. Ivermectin is cheap, it’s used in all parts of the globe that are plagued by parasitic diseases and is generally safe and well-tolerated, when used as prescribed, according to the U.S. Centers for Disease Control and Prevention.

Why did people start using it to treat COVID?

Early in the pandemic, Australian researchers reported that, in lab experiments, ivermectin could slow the reproduction of SARS-CoV-2. The FDA-approved drug might have a potential for repurposing as a COVID therapy, the authors said. However, the effects seen in the lab would need “major doses in humans,” the Cochrane group said.

In July, a large pre-print study out of Egypt that reported ivermectin reduces COVID-19 deaths was withdrawn over concerns of plagiarism and dataset “anomalies,” but not before it had been viewed more than 150,000 times and cited widely, Nature reported.

In the U.S., prescriptions for ivermectin have increased 24-fold from pre-pandemic levels. In addition to onchocerciasis (river blindness), ivermectin is approved for intestinal strongyloidiasis, roundworm infections. Topical formulations can also be also used for head lice and the skin condition rosacea.

There have also been reports of people ingesting veterinary formulas intended for horses, sheep and cattle, which don’t require a prescription. Purchases have increased and the owner of a Calgary feed store was forced to hide his stock of the dewormer after getting numerous calls. In the U.S., hospitals have treated people who bought ivermectin “of unknown strength” off the internet.

“That is so dangerous and so unsupported by real science,” said Montreal infectious diseases specialist Dr Donald Vinh.

But could it work?

A review published by the Cochrane Library in May found no reliable evidence to support using ivermectin for COVID-19 outside of well-designed, randomized controlled studies. The authors couldn’t conclude whether ivermectin leads to fewer or more deaths, or worsens or improves symptoms, compared to no drug or the usual care.

However, a large international trial co-led by McMaster University’s Edward Mills looking at drugs that might be repurposed to treat COVID found ivermectin had “no benefit whatsoever” at reducing emergency room visits or hospital admissions in high-risk adults, Mills said Friday. The randomized trial involved more than 1,300 people recruited predominantly from Brazil. The results haven’t been published or peer-reviewed.

“The advocates of (ivermectin) are putting a great emphasis on the unreliable evidence,” said Mills, a professor of health research methods. “They claim that there are 63 studies that all point in the direction of favourable effects. But no individual study provides any clear evidence of benefits (and) there are not 63 randomized clinical trials,” he said.

“Ivermectin advocates pool effects from observational studies that are very questionable, and from randomized controlled trials that may or may not be randomized and, in general, are poorly conducted and, in some cases, fraudulent,” Mills said.

What could happen if you take livestock doses of ivermectin?

Bad things. Ivermectin overdoses can cause nausea, vomiting, diarrhea, hallucinations, blurred visions, tremors, abnormally rapid breathing, seizures, coma and death. Poison control centres have received a steep jump in calls about people ingesting veterinary formulations. Florida Poison Control tweeted Wednesday that it had treated a total of 39 people for ivermectin exposures in August, most involving ivermectin meant for livestock.

Why are people pushing, and taking it?

Ivermectin advocates claim governments, politicians, “Big pharma” and mainstream media are suppressing evidence that the drug is effective. Ivermectin is a favourite of anti-vaccine conspiracy theorists who claim COVID could easily be controlled with cheap, off-patent drugs like ivermectin, instead of “untested and dangerous” mRNA biological agents. Rogan “also took monoclonal antibodies (lab-made antibodies that target the virus) and yet describes his positive outcome to ivermectin,” Mills said. “That’s a very big stretch of the imagination.”

It would be wonderful if there was “such a simple solution” to COVID, Schwarcz said. Based on the evidence available, the advice not to self-medicate with ivermectin for COVID is sound, he said. Taking large doses of ivermectin is dangerous. Taking ivermectin formulations meant for cattle or horses is seriously dangerous.

“Should further studies, and a number are underway, show that ivermectin is indeed effective at curbing the symptoms of COVID, that advice will change,” Schwarcz said. “That is the way of science.”

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