I don't really understand where you are coming from here. Ivermectin has been around for 40 years and billions of doses have been served to people and it is understood to be a well tolerated drug. No one is saying to go and find some sheep dip and knock back a few schooners of it and see how you go, or get some tablets meant for animals and just self dose. There is more science to it than that and appropriate human dosing is known and understood.
I am aware of cases where people have taken tablets designed for large animals, but why would anyone do that? Why not go to a doctor and ask for a prescription? As with any medication, there may be conflicts with any other medications being taken etc so it would always be sensible to have this done via a physician. Probably did not happen that way in India and other countries, but it would be more sensible to use the physician channels if there was any doubt about what the side effects may be for a normal dose. A bit of common sense is always helpful.
