The Food and Drug Administration says male infertility is not a known side effect of the antiparasitic medication ivermectin. Dubious claims that the drug sterilizes 85% of male users were incorrectly attributed to a questionable 2011 study of the drug’s effect on a small sample of Nigerian men with onchocerciasis, a tropical disease also known as “river blindness.”
As an increasing number of people in the U.S. have turned to the antiparasitic drug ivermectin to try to prevent or treat COVID-19, social media posts have claimed that the medication — which has not been proven to be effective against the disease — could impact the reproductive health of men.
“TIL Ivermectin apparently sterilizes the majority (85%) of men that take it,” reads a since-deleted Sept. 5 tweet that was turned into an image and shared on Facebook, for example.
Another Facebook post commenting on the drug included a screen capture of the headline of a KTSM-TV story that also has been retracted.
“Ivermectin causes sterilization in 85 percent of men, study finds,” was the heading of that Sept. 8 article.
But that was not the conclusion of the 2011 Nigerian study mentioned in the article or linked to in the tweet.
The introduction section of that study said a different report published in 2002 found that “85% of all male patients treated in a particular centre with ivermectin in the recent past” developed “sperm dysfunctions,” such as low sperm counts and poor sperm motility or movement.
However, the 2011 study didn’t say that the sperm dysfunctions mentioned in the 2002 report meant that those men were suddenly infertile.
“I don’t think the study conclusively provides any evidence to show that ivermectin causes infertility,” Dr. Puneet Masson, director of Male Reproductive Medicine and Surgery at Penn Medicine Urology, told FactCheck.org in an interview.
Ivermectin, in tablet form, has only been approved by the Food and Drug Administration for use in humans to treat certain parasitic worms. A topical formulation has been approved by the FDA for external use against parasites such as head lice and for skin conditions such as rosacea.
There is also an FDA-approved version of ivermectin to treat certain internal and external parasites in animals. But animal drugs should never be taken by humans, the FDA says.
As for side effects, the FDA does list several that have been associated with ivermectin for people, such as skin rashes, nausea, vomiting, diarrhea, stomach pain, swelling, dizziness and seizures. But male infertility or sterility is not one of them.
“Infertility in men is not a known side effect of ivermectin and is not included as a side effect in the labeling,” an FDA spokesperson said in an email to FactCheck.org. “The labeling for ivermectin and its bioequivalents states that ivermectin had no adverse effects on the fertility in rats in studies at repeated doses of up to 3 times the maximum recommended human dose of 200 mcg/kg (on a mg/m2/day basis). ”
The FDA’s statement, along with other factors, led the El Paso, Texas-based news station to pull its article.
“FOR THE RECORD: A national story regarding Ivermectin and a study regarding its effect on men’s reproductive health that KTSM published, has been removed from our website,” KTSM investigative reporter Erin Coulehan, the author of the original story, wrote in a Sept. 9 correction. “Concerns over the scientific research methods, the veracity of the original, peer-reviewed report and public statements by the Food and Drug Administration (FDA) saying that infertility is not a known side effect of Ivermectin all led to our editorial decision to remove the story.”
Despite the retraction — and numerous fact–checking articles casting doubt on the claim — people on social media continue to assert that ivermectin makes men sterile.
The Nigerian Study
The 2011 study was published in the Archives of Applied Science Research, which is purported to be a “peer-reviewed, open-access journal.” A copy of the study is available online via the Scholars Research Library.
The authors tested the effect of ivermectin on the sperm functions of a small number of Nigerian men who were given the drug for 11 months to treat onchocerciasis, a tropical illness also known as river blindness, which is caused by parasitic worms transmitted through repeated bites by blackflies.
While 385 men with the disease were initially screened for the study, only 37 of them — between the ages of 27 and 58 — had normal sperm counts that made them eligible for further testing. The other men with “very low sperm counts” were excluded.
Subsequently, the authors “observed significant reduction in the sperm counts and sperm motility of the patients tested,” but did not “record any significant change or alteration in the sperm viscosity, sperm volume, and sperm liquefaction time of the patients.”
Overall, the authors said, the results indicated the drug could cause infertility in the patients, which led the researchers to “suggest that caution be seriously exercised in the treatment of male onchocerciasis patients with ivermectin to avoid the adverse effects it has on the patients’ sperm functions.”
But Masson, who is also an assistant professor of clinical urology in surgery at the University of Pennsylvania, told us the study had several issues.
His primary concern was the sample size and the health of the patients.
“They threw out basically more than 90% of their study patients that were in their dataset because they had abnormal semen parameters,” he said. “So my question is: Is something but the underlying disease causing people to be infertile?” (The study did not include a control group of patients with the disease who did not receive ivermectin.)
He also said that while the study did show some of the men had a “numerical decline” in their sperm concentration and motility, which are measurements of the amount and movement of the sperm, it wasn’t a “clinically significant” decrease, because the numbers didn’t drop below the “normal values” used for comparison in the study.
That would not make the men infertile, Masson said, noting that the study did not include any actual pregnancy data to suggest that the men had difficulty achieving a pregnancy compared with anybody else.
As we pointed out earlier, the authors of the study did not say ivermectin causes sterility in 85% of men — which is how many promoted their research online. The 85% statistic — which was worded differently — was mentioned in the study’s introduction, but was attributed to another source.
“A recent report showed that 85% of all male patients treated in a particular centre with ivermectin in the recent past who went to the laboratory for routine tests were discovered to have developed various forms, grades and degrees of sperm dysfunctions,” the authors wrote. No other details about the report were provided in the 2011 study.
A footnote indicated that the source was a 2002 paper published in the Journal of Biomedical Investigation, but we could not find it by accessing online databases for journals, or when doing an internet search. The African Journals Online resource has some archived editions of the journal, but only going back to 2003 — when AJOL says the first volume was published.
We tried contacting the authors of the 2011 study for comment on their work — and to obtain a copy of the 2002 report they referenced — but we did not receive a response.
What we do know is that the 10-year-old Nigerian study alone is not evidence that ivermectin makes the vast majority of male users sterile. And without more information about the 2002 report, it’s not possible to say if it supports the claim, either.
Editor’s note: SciCheck’s COVID-19/Vaccination Project is made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation. The goal of the project is to increase exposure to accurate information about COVID-19 and vaccines, while decreasing the impact of misinformation.
Food and Drug Administration spokesperson. Email sent to FactCheck.org. 10 Sep 2021.
Dr. Puneet Masson, director of Male Reproductive Medicine and Surgery at Penn Medicine Urology. Interview with FactCheck.org. 17 Sep 2021.
Centers for Disease Control and Prevention. “Rapid Increase in Ivermectin Prescriptions and Reports of Severe Illness Associated with Use of Products Containing Ivermectin to Prevent or Treat COVID-19.” CDC.gov. 26 Aug 2021.
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