Mostly vomiting stops on its own and people don't die. Even when someone dies, it won't break the beliefs of survivors because they don't believe it works 100% of the time anyway. In your case, you even took an ineffective dose of Emetrol but still believed in its effectiveness despite that! How many ineffective doses would it take for you to not credit Emertol with stopping the vomiting?

If there's a scientific study, that might show something better than the giant fail-fest of cultural medical knowledge. I don't know of any human society that hasn't at least historically had a bunch of ineffective medicine that was widely used. Even modern western society probably has some - such as this Emetrol perhaps or wrong results of drug trials. An extreme case is China where normal doctors in hospitals routinely prescribe herbal remedies alongside conventional medicine.