Ivermectin is the latest drug being floated as a treatment against the coronavirus despite warnings from public health authorities and a lack of evidence that it works. But a claim circulating on Facebook says the anti-parasitic drug has the side effect of sterilizing men who take it.

An image shared on Facebook shows a man laughing, and on top of the picture is text that reads, “When you find out Ivermectin sterilizes the majority (85%) of the men who take it.

Similar claims have been shared several times across social media as the drug has seen a sharp increase in use.

The post was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)

While the FDA has identified several potential side effects of ivermectin, including nausea, vomiting and dizziness, infertility in men is not listed.

The 85% figure comes from a questionable source.

An obscure, outdated study

The 85% figure cited in the Facebook image and the other social media posts comes from a 2011 study conducted in Nigeria by researchers looking at the effect ivermectin had on fertility in men with onchocerciasis, also known as river blindness.

Researchers screened 385 men with the condition, ultimately choosing 37 people to participate in the study as “their sperm counts were normal while the remaining patients had very low sperm counts.”

The men were studied for 11 months as they were treated with the drug, and researchers found a “significant reduction in the sperm counts and sperm motility of the patients tested.”

However, there are several issues with the study.

While the study began with 385 men, only 37 ended up being monitored for their ivermectin use — a sample size too small to draw any serious conclusions about the drug’s impact on fertility.

The study also lacked a control group to see whether it was the drug that had an effect on the men’s fertility, or some other factor, such as their river blindness.

The 85% figure was also not the conclusion reached by the study. It was mentioned only in the introduction of the paper as the findings from a separate report of men who were tested outside of the study and found to have “developed various forms, grades and degrees of sperm dysfunctions.”

The journal the study was published in, the Archives of Applied Science Research, claims to be a peer-reviewed, open access journal, but no information could be found on the journal’s peer-review process.

The publication date of the study could not be found.

What is ivermectin?

Ivermectin tablets are used to treat conditions caused by parasitic worms in humans, such as intestinal strongyloidiasis and onchocerciasis, according to the Food and Drug Administration. Topical ivermectin is also used for head lice and to treat skin conditions like rosacea.

A separate formulation of ivermectin is available for veterinary use, and is used to treat parasites in animals and to help prevent heartworm disease.

The United States has recently seen a sharp increase in people using the drug to combat COVID-19. The trend has been fueled by claims that the drug is a miracle treatment for the virus.

The FDA, Centers for Disease Control and Prevention and the World Health Organization have warned against using ivermectin.

The drug can negatively interact with other medications and could lead to overdoses if improperly used.

“The FDA has not authorized or approved ivermectin for the treatment or prevention of COVID-19 in people or animals,” the FDA said in a statement. “Ivermectin has not been shown to be safe or effective for these indications.”

Ivermectin use has risen so much that pharmacies across the United States have reported shortages of the anti-parasitic. As a result, more people are buying the animal version of the drug from livestock supply stores, the New York Times reported. The animal version is geared toward larger animals such as horses, and comes in a highly concentrated liquid or paste.

A CDC-issued health advisory reported a “five-fold increase” in the number of calls made to poison control centers related to misusing ivermectin during July. Several calls involved people who took the animal version of the drug and had an overdose.

Our ruling

A Facebook post shared a repeated claim that 85% of men who take ivermectin become sterile.

The source for the 85% figure is a study conducted 10 years ago and used a small sample size with no control group to compare the results. The figure also wasn’t the conclusion reached by the study, and was only referenced in the paper as being from a separate report.

The peer-review process of the journal the study was published in is also questionable.

The anti-parasitic drug has seen increased use during the pandemic as some people claimed it was a miracle treatment for COVID-19. However, there is no proof that ivermectin is effective against the virus.

We rate the infertility claim False.

This fact check was originally published by PolitiFact, which is part of the Poynter Institute. It is republished here with permission. See the sources for this fact check here and more of their fact checks here.