On Thursday the Centers for Disease Control and Prevention issued a new warning against using the drug ivermectin to treat COVID-19. The drug is FDA-approved to treat a narrow range of parasitic infections including onchocerciasis (or river blindness) and strongyloidiasis. It’s also used to treat head lice and rosacea, and veterinarians often prescribe the drug to treat parasitic infections in animals as well. If administered incorrectly and at the wrong dose, it can cause nausea, vomiting, and diarrhea and, in the worst cases, hypotension, confusion, or even death, according to the CDC report.

Since the pandemic began, researchers have been investigating using ivermectin to treat COVID-19, as very early and preliminary data hinted that the drug might kill viruses. In June of last year, researchers reported in the Journal Antiviral Research that ivermectin was successful in stopping the replication of SARS-CoV-2 in cells in a petri dish. But, importantly, the dosage necessary to achieve this was extraordinarily high, and if given to humans would likely have dangerous, if not deadly side effects. 

Despite this, the idea that ivermectin helps treat COVID-19 became quite popular during the pandemic, prompting the FDA to issue a warning against its use in March of 2021. To date, no large-scale clinical trial has found ivermectin to be effective against COVID-19, and researchers have largely dismissed it as a research target. 

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Even with this lack of evidence, it seems prescriptions for ivermectin in the United States are at an increased level. According to the CDC report, “a recent study examining trends in ivermectin dispensing from outpatient retail pharmacies in the United States during the COVID-19 pandemic showed an increase from an average of 3,600 prescriptions per week at the pre-pandemic baseline (March 16, 2019–March 13, 2020) to a peak of 39,000 prescriptions in the week ending on January 8, 2021.” And in early July of 2021, according to the report, there was another spike in prescriptions, increasing to 24 times the number of pre-pandemic prescriptions of ivermectin. 

The most concerning issue with ivermectin is the dosage. In many instances, people who have taken ivermectin have taken doses and formulations meant for veterinary use, not human use. Because they are intended for large animals like cows or horses, the concentrations of these are quite high. As the CDC notes, many of these formulations “may also contain inactive ingredients that have not been evaluated for use in humans.” Taken at these levels, the drug could be toxic. In January 2021, the CDC’s poison control centers got three times as many calls about ivermectin than they did pre-pandemic. 

While it may sound disappointing that this drug was unable to help treat COVID-19, the reality is that 18 months into this pandemic, we have many treatments at our disposal. The best ones are the vaccines, which prevent most cases of COVID-19 in many people and prevent nearly all severe cases of the disease that would otherwise require hospitalization. So getting vaccinated means you are far more likely to avoid needing any drugs to treat COVID-19 than you would be if you weren’t vaccinated. You can read more information about the vaccines and their safety here