When doctors and scientists scoured for a COVID-19 cure during the early days of the pandemic, initial studies suggested a number of potential remedies that turned out to be bogus. But few dubious solutions have had the staying power of ivermectin, an antiparasitic drug used to treat large farmyard animals.

Ivermectin has been promoted as an “alternative” COVID cure by the likes of podcast host Joe Rogan—who has supported the horse deworming drug over COVID vaccines, even using it himself—and doctors have prescribed the treatment to COVID patients. In small doses, ivermectin can be prescribed to treat head lice or other parasites in humans, but the Food and Drug Administration (FDA) has not approved the drug as a COVID treatment.

In the U.S., ivermectin prescriptions soared to 88,000 per week last August, from a baseline of 3,600, prompting the Centers for Disease Control and Prevention (CDC) to issue a warning against using the drug. The CDC said its poison control center had witnessed a fivefold increase in calls related to ivermectin overdoses and adverse effects.

Maybe that madness is coming to an end as, on Wednesday, a large-scale scientific study showed that ivermectin has “no significant effects” in treating COVID.

The so-called TOGETHER study, conducted in Brazil, is the largest clinical trial into the effects of ivermectin on COVID to date and generally supports the findings of smaller studies, which have also found no significant benefit to ivermectin treatment.

The TOGETHER trial took 3,515 COVID patients and randomly assigned treatment of either ivermectin, a placebo, or a third intervention. The study was double-blind, meaning neither the patients nor the doctors knew which of the three options each participant received at the time.

“Treatment with ivermectin did not result in a lower incidence of medical admission to a hospital due to progression of COVID-19 or of prolonged emergency department observation among outpatients with an early diagnosis of COVID-19,” the researchers concluded.

The scientists behind the Brazil trial presented initial results from their experiment last August, but the full peer-reviewed study was published this week in The New England Journal of Medicine.

This story was originally featured on Fortune.com