https://astralcodexten.substack.com/p/ivermectin-much-more-than-you-wanted
This is an extraordinary (and thorough, and lengthy) analysis of the various ivermectin studies that get bandied about, written by the hand of Scott Alexander. (If you've never read an analysis of anything by Scott Alexander before and those sorts of intellectual deep-dives are of interest to you, you're in for a treat).
Here, Scott analyses 30 or so ivermectin studies, and shows which ones are potentially of merit, and which ones are so poorly designed (or outright fraudulent) that they can be dismissed out of hand.
Of the 11 or so studies he finds to have merit, they have very mixed results, with no particularly large effect when considered overall, but: Scott makes an extraordinary observation.
The studies that appear to show some plausible positive effect of ivermectin in treating COVID-19... tend to be in areas of the world where infection with one or more varieties of parasitic worm are common. We know that parasitic infection has an attenuating effect on the immune system, so it's quite possible that Scott has stumbled on to an explanation for why the occasional legitimate study in places like Pakistan or Nigeria shows a positive effect for dosing COVID-19 patients with ivermectin, but studies in the US and/or Europe tend to show no effect.
If you're interested in learning how to read a study, following Scott's 30 examples is a terrific exposition on the topic. If you'd like to skip ahead to the final analysis of the "studies of merit", skip down to the section "Analysis".