Because of a recent in vitro study that examined effects of ivermectin on the coronavirus that causes COVID-19, FDA's Center for Veterinary Medicine has issued a warning letter to veterinarians and other health professionals. The letter stresses that the drug has not been studied in animals or humans and warns people not to take ivermectin intended for animal use.
Because of differences in drug metabolism and recommended dosage rates, formulations intended for use in animals could potentially cause serious harm if taken by people.
The full FDA warning letter on use of animal ivermectin in people is available here. The prepublication research report on ivermectin use in vitro against SARS-CoV-2 can be read here.
More information on the pharmacology and use of ivermectin in animals can be found in the MSD Veterinary Manual.