Note that the FDA does not say don't take it if your doctor prescribes it, they just say in that case you should follow the directions precisely. The problem is the majority of people taking this stuff don't seem to be doing so under medical guidance. That's a serious issue they have a responsibility to address.
There's a fair bit of exaggeration going on, in both directions. Surprise.
I think he might have meant the dosage that it is sold in is different.
Ivermectin for treating parasites is typically supposed to be taken as a single dose. For some parasites it might need to be repeated in 3 to 12 months.
If a doctor prescribes it to treat a human I'd expect the prescription to be for the right amount of pills for your body weight to deliver that single you-sized dose.
Horse ivermectin is sold in a quantity suitable for a 1250 pound horse.
From what I've read it appears that a lot of people buy that horse-sized single dose and use it all. Worse, a lot of them seem to take it daily.
Meanwhile, even if ivermectin worked, it would be secondary to vaccination because you want to prevent as much as early as possible. Should any of those wonder drugs end up working, it wouldn't help ICU capacity much :-(
Neither the dosages nor the active ingredients are different. Both for humans and for animals, the recommended dose of Ivermectin to treat parasites is 200 micrograms per kilogram of body weight. The "active ingredients" are Ivermectin, period.
I have a bottle of injectable Ivermectin intended for cattle here, and it says it's pure Ivermectin in propylene glycol (typical carrier for injectables even for humans). I got it to treat Histomoniasis in our turkeys, which is btw an off-label use, because officially Ivermectin is not supposed to be effective against protozoa, but Histomoniasis is almost 100% fatal in turkeys and I haven't lost one since starting to give them Ivermectin as soon as I notice they have it. I've found that if I give them 600 micrograms/kg body weight every other day 3 times, they recover fully. What does this have to do with Covid? Only that a) Ivermectin works for some things other than those for which it's officially "blessed", b) at least in turkeys a much larger than normal dose doesn't seem to have any ill effects. As for the dose, I decided that it was probably safe for our turkeys because I read a paper where they gave that dosage to humans to combat malaria by making those humans lethally toxic to the mosquitos. The paper said the dose was "well tolerated". If they can do that to their human patients I can do it with my turkeys.
I'm not planning to inject myself with my veterinary Ivermectin even if I did come down with Covid... because I agree that so far the evidence that it's helpful isn't very strong. But I also think that this article is quite laughable... basically it says "Why You shouldn't use Ivermectin to treat or prevent Covid: because, uh... because we haven't said it's OK to do so." Sorry CDC, but your credibility just isn't /that/ high. And going to a hospital for /anything/ is also really dangerous... almost certainly more so than a couple of doses of Ivermectin.