Ivermectin has helped treat hundreds of millions of people and billions of pets and farm animals for parasitic diseases. Its discovery even garnered a Nobel Prize in Physiology or Medicine in 2015. But now several groups of doctors are encouraging and enabling people to take the drug off-label to treat or prevent COVID—despite a lack of solid evidence that it works against the disease and the fact that high doses can be harmful. In doing so, some experts believe these groups are undermining vaccination efforts.

Derived from a compound discovered in a soil microbe in Japan, ivermectin has been called a “miracle drug” and “the penicillin of COVID” by Pierre Kory, a critical care physician in Madison, Wis. Kory is president of the Front Line COVID-19 Critical Care Alliance (FLCCC), a group of physicians and scientists who champion ivermectin, along with other drugs and vitamins with dubious efficacy against COVID. The organization, along with two others called the British Ivermectin Recommendation Development (BIRD) Group and America’s Frontline Doctors (AFLDS), have drawn criticism from many other physicians and scientists. Yet treatment protocols, links and videos from these groups are sweeping through social media, promoted by vaccine skeptics.

The notion that ivermectin is a miracle medicine gives people who reject vaccines a false sense of security, says Daniel Griffin, a physician and infectious disease researcher at Columbia University and Chief of the Division of Infectious Disease at the company ProHEALTH. A recent poll by the Economist and YouGov indicated that a total of about 56 percent of people who believe ivermectin is effective against COVID either do not plan to get vaccinated or are unsure about the vaccine. But unlike the data supporting vaccines, Griffin says, the evidence behind that use of ivermectin is questionable and unclear. He worries not only that the hype over the antiparasitic drug may keep some people from getting vaccinated but also that sick people taking it at home might delay going to a hospital and miss the efficacy window for evidence-based COVID treatments.

Nevertheless, ivermectin prescriptions are soaring, topping 88,000 a week in the U.S. last month (compared with an average of 3,600 per week in 2019). Although the form of the drug sold in pharmacies is routinely prescribed for U.S. Food and Drug Administration–approved uses such as treating parasitic infections, the doses and schedules that the FLCCC posts on its Web site are not consistent with those typically advised for humans. Cedric Dark, an emergency physician and professor at Baylor College of Medicine, says ivermectin is usually given as a one-time dose when it is used as a parasite treatment. In contrast, the FLCCC’s prevention protocol suggests taking it “twice a week for as long as [COVID] risk is elevated in your community.” But Griffin explains that “we do not have reliable safety data on the prolonged courses being recommended currently or in patients taking ivermectin while suffering from COVID-19 and all the immune and metabolic changes associated with this disease.”

Ivermectin was not the first drug the FLCCC endorsed for treating COVID. Paul Marik, a critical care physician and professor at Eastern Virginia Medical School, helped found the organization. In 2016 he had begun giving what became known as the “Marik cocktail” for treating sepsis, a life-threatening reaction to an infection that triggers inflammation throughout the body. The intravenously deliveredcocktail contains a high dose of vitamin C, the steroid hydrocortisone and vitamin B1. A randomized trial ultimately showed the cocktail was ineffective for sepsis. But when the pandemic hit, Marik began trying it on patients with COVID. In April 2020 he, Kory and a few of their colleagues formed the FLCCC to encourage the adoption of a modified cocktail that they thought could work for the disease. And in late 2020 the group added ivermectin to its protocols.

Much of the public interest in ivermectin as a treatment and prophylactic for COVID can be traced to a study led by Australian scientist Leon Caly that was in the spring of 2020. In that work, scientists added very high concentrations of the drug to cells grown in petri dishes and reported that it prevented the virus that causes COVID from making copies of itself. Similar studies in the past have indicated that ivermectin has antiviral properties when added to lab-grown cells: it blocked replication of viruses that cause dengue, Zika, West Nile, AIDS and other diseases. Prior to the pandemic, however, only one clinical trial had evaluated ivermectin specifically for a viral illness (dengue fever), and it showed no clinical benefit.

Nevertheless, clinical trials testing ivermectin for preventing or treating COVID began, “driven by a very generous motivation to try to find inexpensive cures that are going to prevent people from dying [of COVID],” says public health expert Howard Forman of Yale University. But the trials used different doses on different schedules, Dark says, “which makes it very difficult to compare one to the next.”

Furthermore, he says, many of the ivermectin studies have design flaws that preclude them from leading to changes in clinical practice. A report published in July by Cochrane, a highly regarded independent organization that reviews medical research and helps guide clinical practice, looked at dozens of studies on ivermectin, of which only 14 qualified for evaluation. The report excluded 38 investigations because of problems with their methodology: they either had no control group, an inappropriate control group or other kinds of biases. The 14 remaining studies, which included a total of 1,678 participants, did not support the use of ivermectin for preventing or treating COVID, the report concluded.

In contrast with ivermectin, the evidence of COVID vaccines’ effectiveness is “incredibly compelling,” Griffin says, and the majority of COVID deaths and hospitalizations are vaccine-preventable.

Yet the groups promoting ivermectin do not appear to strongly support the COVID vaccines. The FLCCC says little about them on social media and writes in the current version of its prevention protocol that ivermectin is a “safety net” for those who are not vaccinated (although that protocol adds, “Vaccines have shown efficacy in preventing the most severe outcomes of COVID-19”). AFLDS founder Simone Gold, a doctor who was arrested for activities related to her involvement in the January 6 insurrection at the Capitol and is connected to a conservative political group, and Tess Lawrie, director of a company called the Evidence-Based Medicine Consultancy and organizer of the BIRD Group, have even shared vaccine misinformation in videos online. And AFLDS also gives advice on vaccine exemptions on its Web site.

Additionally, the AFLDS Web site suggests—without evidence—that there is some nefarious reason that vaccines are heralded while cheap drugs and dietary supplements (such as ivermectin, hydroxychloroquine, zinc, vitamins and antibiotics) are not. The FLCCC, too, has alluded to a conspiracy in a tweet: “The FDA, the CDC, major media & others hope you’ll believe them when they tell you that [ivermectin] was meant only for animals, & that it’s dangerous to use for [COVID].”

Heidi Larson, director of the Vaccine Confidence Project at the London School of Hygiene & Tropical Medicine, calls this approach “a classic tactic to undermine confidence in authority.” She adds that such “manipulation is really a core strategy across the groups that are trying to undermine confidence in vaccines.”

Dark points out that a cheap, widely available drug is used to treat symptoms of COVID: a steroid called dexamethasone. When a well-designed clinical trial showed that dexamethasone helped certain patients hospitalized with COVID, it was widely adopted by physicians. Griffin says the anticoagulant medication heparin is another example of a cheap drug being used in hospitals to help treat COVID patients.

Ivermectin can be a moneymaker, too. AFLDS charges $90 for telehealth visits with doctors willing to write off-label prescriptions for ivermectin or hydroxychloroquine—another highly touted drug that was found to be ineffective and sometimes harmful—for treating COVID. And AFLDS connects people with a digital pharmacy that will fill those prescriptions or send them to a local pharmacy, sometimes for exorbitant prices. Contacted for this story, the group declined to comment on these practices. The FLCCC also curates a list of pharmacies that will fill off-label ivermectin prescriptions, and it offers a list of physicians who use the group’s protocols. The organization did not respond to requests for comment, including on whether it earns money through these services.

Despite claims of a conspiracy against ivermectin, Griffin points out that researchers are continuing to study it and other repurposed drugs for COVID. There are at-home randomized placebo-controlled clinical trials underway, including the COVID-OUT trial, the ACTIV-6 study and the U.K.-based PRINCIPLE trial.

“I would love for ivermectin to work. Just prove it,” Forman says. But even if we have an effective treatment for a disease, that does not negate the need for a vaccine, Larson says. “We need all the tools in the toolbox,” she adds.