Male sterility isn’t a proven side effect of ivermectin, contrary to claims by social media users

Ivermectin sterilizes the majority (85%) of men that take it
Inadequate support: A study reporting reduced sperm quality in patients treated with ivermectin only looked at a very small group of patients, and didn’t compare results with a control group that was untreated with ivermectin. Several animal studies show no negative effect on sperm quality.
Misrepresents source: The study did not conclude that 85% of patients became sterile after taking ivermectin. Instead, the study referred to an earlier report, which suggested that 85% of patients treated with ivermectin were found to have changes in their sperm. That report was affected by several issues.
Ivermectin is a broad-spectrum anti-parasite drug approved for use in treating parasitic diseases, such as river blindness and strongyloidiasis. While there have been a handful of reports about altered sperm quality in humans and rats treated with ivermectin, these studies were affected by certain issues such as a lack of a control (untreated) group and small sample sizes. Based on the overall scientific evidence available to date, the U.S. Food and Drug Administration doesn’t consider sterility to be a side effect of ivermectin.

FULL CLAIM: Ivermectin sterilizes the majority (85%) of men that take it


Ivermectin, a drug approved for treating parasites in animals and humans, has been touted as a supposed cure for COVID-19. However, ivermectin hasn’t been approved for treating COVID-19 outside clinical trials in the U.S., the European Union or Britain. As described in previous reviews by Health Feedback, clinical trials haven’t found ivermectin to be effective against COVID-19.

In September 2021, social media posts appeared claiming that ivermectin is linked to male sterility (see here, here, and here). Many of the social media posts making this claim cited a study published in 2011. This study evaluated the effect of ivermectin on the sperm of 37 men in Nigeria, who were diagnosed with onchocerciasis, or river blindness, a disease caused by parasitic worms. The authors evaluated the sperm before treatment and after 11 months of ivermectin treatment. They observed reductions in sperm counts, sperms’ ability to move and sperm shape in these patients after ivermectin treatment. However, the researchers didn’t further analyze the sperm of another 384 patients (90.4% of participants originally recruited for this study), as they had “very low sperm counts” or were otherwise not suitable for further tests.

This small sample size, along with the authors’ excluding over 90% of samples, “means it is impossible to draw any firm conclusions”, wrote Gideon Meyerowitz-Katz, an epidemiologist and PhD student at the University of Wollongong in Australia, on Twitter.

In addition, unlike well-controlled randomized trials, the 2011 study didn’t include a control group, as the researchers didn’t examine the sperm quality of men who weren’t treated with ivermectin, to control for other effects which may affect sperm quality of motility, such as the disease itself. “[M]y guess would be that the authors were surveilling a very unwell population who happened to be taking ivermectin. Hard to tell if the medication contributed to that at all,” Meyerowitz-Katz added.

In fact, the 85% figure repeated in many claims is not a conclusion from the 2011 study. The figure actually came from the introduction of that study, which cited a report published by two of the authors in 2002. According to the 2011 study, this previous report from 2002 found 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”.

We weren’t able to locate the 2002 report cited in the 2011 study and as such, were unable to assess the quality of the study. However, given the description of this report in the 2011 study, it may also contain the same issue pointed out by Meyerowitz-Katz, specifically that the report examined only a population that was unwell to begin with and had no untreated group with which to make comparisons. Curiously, the journal in which the 2002 report was allegedly published is the Journal of Biomedical Investigation, based on the relevant citation in the 2011 study. However, this journal published its first volume in 2003, a year after the 2002 report was published.

Another study in male rats is also sometimes referred to in claims regarding ivermectin and male fertility[1]. This  2017 study, which reported reduced sperm count and motility in rats treated with ivermectin, was also cited in posts making the same claim[1]. However, only 16 rats were treated with ivermectin in this study, a small sample size from which it can be hard to draw conclusions. No negative effect on sperm was reported in a 2019 study on rabbits, a 2001 study on horses and  a 1987 study on beagles [2,3,4]. However, all these studies only included a similar small number of animals. Therefore, the animal studies cannot be considered conclusive.

In the U.S., ivermectin is approved for the treatment of onchocerciasis (river blindness) and intestinal strongyloidiasis. Ivermectin is also approved for the treatment of head lice and rosacea (to be applied to the skin). According to the FDA., known side effects of ivermectin include skin rash, nausea, vomiting, diarrhea, stomach pain, facial or limb swelling, neurologic adverse events (dizziness, seizures, confusion), sudden drop in blood pressure, severe skin rash potentially requiring hospitalization and liver injury. Regarding fertility, the approved labelling of ivermectin 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 study used to substantiate claims that ivermectin treatment causes male sterility is flawed, and suffers from a small sample size and the lack of a control group. The claim that ivermectin causes a majority of male patients to become sterile is unsupported by the scientific evidence.




Published on: 14 Sep 2021 | Editor:

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