One option has been endorsed by scientists, regulators, academic institutions, public health experts, and government leaders alike and proved remarkably effective as vaccines have been doled out to billions of people across the world less than a year into the outbreak; the other has a handful of approved uses in humans but no robust clinical evidence that it works against coronavirus illness, a fact the aforementioned experts repeatedly raise while warning against its off-label use for COVID. Which one of these would you take? And, more importantly if you’re going the equine dewormer route, why?

It’s a head-scratcher as a small but growing number of Americans—many of them from the anti-vaxxer or vaccine skeptic crowd—have pushed demand for ivermectin prescriptions (and the version for animals) into high gear over the past few months. This medical counterculture harbors an abiding belief that the efficacy and safety of COVID vaccines is overblown as well as a mistrust of pharmaceutical companies, government officials, and media narratives around the pandemic. The politicization of COVID public health efforts certainly doesn’t help matters since ideology is one of the strongest indicators of whether or not someone is a COVID vaccine skeptic. There were usually about 3,600 ivermectin prescriptions issued weekly in the U.S. prior to the pandemic; by mid-August, that number had jumped to 88,000 per week.

This is despite the fact that the Food and Drug Administration (FDA), the World Health Organization (WHO), and the very maker of ivermectin itself, pharma giant Merck, have all urged people not to go out and take large amounts of a livestock-focused drug to stop the coronavirus given the sheer lack of evidence it works and the very real risks of overdoses and hospitalization (the WHO recommends against any type of COVID-related ivermectin use outside of a clinical trial). The FDA is a bit more blunt and points out that ivermectin isn’t even meant to fight viruses.

“FDA has not approved ivermectin for use in treating or preventing COVID-19 in humans. Ivermectin tablets are approved at very specific doses for some parasitic worms, and there are topical (on the skin) formulations for head lice and skin conditions like rosacea. Ivermectin is not an anti-viral (a drug for treating viruses),” the agency says, noting reports of more people landing in the hospital from ivermectin overdoses. (It turns out your typical human shouldn’t take similar doses of a treatment as what’s given to a 1,000 pound horse.)

Mistrust in institutions and mainstream narratives is nothing new among certain slices of the populace. But why pair that mistrust with advocating for a completely different drug? Scottish psychologist and public health communicator Stuart Ritchie, a lecturer at King’s College London, has a fairly simple assessment of what’s driving the current ivermectin frenzy, much like the clamoring over hydroxychloroquine, an unproven treatment for COVID touted by former President Donald Trump.

“The reason for the double-standard is obvious: contrarianism. Treatments such as ivermectin (and hydroxychloroquine and Vitamin D) have never had mainstream approval, or the nod from U.K. or U.S. medical regulators for their use against COVID,” he wrote in a recent column for the NewStatesman. “The contrarians can get excited about the apparently dramatic effects of ivermectin without having to agree with people they regard as wildly wrong on case rates, death rates, the effects of lockdowns, and so on. They also get to feel the frisson of telling the world that they know better: they have secret knowledge about a super-important treatment, and the blinkered medical community just won’t listen.”

Numerous studies delving into the psychology of vaccine skeptics pick up on this contrarian bent, including significant evidence that presenting facts and data to anti-vaxxers typically makes them double down on their scientifically invalidated positions. It turns out that same quirk of psychology can also lead some people to champion an obscure animal drug in an act of epistemological defiance, especially when they can point to validation from politically charged organizations like America’s Frontline Doctors and the social media feeds of like-minded people.

The ivermectin-for-coronavirus crowd is still a pretty small slice of the population. But it’s a vocal one with the ability to reach millions of people via social media and drive unnecessary hospitalizations from overdoses in a moment when ICUs are already at the breaking point from treating COVID patients.