An old study supposedly reporting that ivermectin — already in the headlines — causes sterility in 85 percent of men has gained traction online this month. However, there are many reasons to doubt the claim. If ivermectin does any damage to male fertility at all, and that's a big if, the size of the effects are probably much smaller than are being reported.
The anti-parasite drug ivermectin has become the latest culture war flashpoint, and that means plenty of people have become motivated to distort the truth about it. Most of that comes from people exaggerating the benefits found against COVID-19 in small studies to claim it removes the need for vaccination. There is absolutely no evidence for that, but that doesn't mean appropriate doses for appropriate treatment are particularly dangerous. Misappropriating its uses for, say, COVID, however, is dangerous, the FDA has warned.
Over the last few days, reports have circulated on social media, picked up by some news outlets, of a study from 2011 reporting 85 percent of Nigerian men being treated for river blindness with ivermectin were at least partially sterilized.
The study describes serious consequences for male fertility from taking ivermectin. However, the 85 percent figures comes not from this study itself, but a 2002 cited paper by overlapping authors. The earlier work does not appear to be available online, and may well not exist. The 2011 paper, however, comes with some major red flags.
For a start, it was published in Scholars Research Library. Although it claims to be peer-reviewed, Scholars Research Library bears some hallmarks of a “predatory journal”, which is a place that will publish anything that is submitted — for a fee. These journals do not require proper academic standards for publishing, such as peer-review, and unscrupulous researchers use predatory journals to pad their resumes with work that wouldn't get published under true review.
The 2011 study also lacks any acknowledgment of its limitations, usually a bad sign for a medical paper, and lacked a control group. Although described as being on 385 patients, most of these were excluded for pre-existing low sperm counts, so the effects of ivermectin were only investigated in 37 individuals. The fact sperm counts were so low among men suffering river blindness before they were put on ivermectin indicates it may not be the drug that is the problem.
Snopes has tried to contact the Nigerian universities at which the authors claim to be based to see if they actually worked there, but have so far had no reply.
However, the biggest warning sign is that ivermectin is not a new drug. Besides being widely used as a de-wormer for livestock in the West, it has treated so many people for tropical parasites its discovery was recognized with a Nobel Prize. If most of the men who have taken it over the last four decades had become sterile as a result, it's a safe bet there would be more than one study revealing that fact.
That doesn't rule out rarer effects. If ivermectin was causing very infrequent cases of infertility it could take a long time for anyone to notice. Indeed, a 2008 study on its effects on infertility in the peer-reviewed Environmental Toxicology and Pharmacology reports “slight effects” of ivermectin alone on rats, but more substantial ones when taken together with verapamil, used to treat high blood pressure. Other animals may be similarly affected.
It's not impossible subtle effects, or more serious ones in combination with other drugs, could have stayed under the radar this long, but an 85 percent fall in fertility for ivermectin alone is implausible.
Meanwhile, research continues as to whether ivermectin has any benefit against COVID-19, with studies so far producing conflicting results, though none of what has been published justifies the hype.
On the other hand, memes presenting ivermectin as a drug purely for animals may be fun, but in the cause of evidence based medicine, two wrongs don't make a right.