Ivermectin is a broad spectrum anti-parasite medication. It is most widely used to combat river blindness but works against a wide variety of ringworms, mites and lice as well, including strongyloides. It cannot be used against tapeworms.
Ivermectin is derived from a chemical found inside some bacteria. The chemical interferes with muscle function and the ability of nerves to refrain from firing. This combination will eventually kill most small multi-cellular life forms. The drug may have the same effect in humans and other mammals who are treated with the veterinary version of the drug, causing ataxia and other muscle control symptoms, but these are rare and generally non-life threatening in mammals. However, some breeds of dog are particularly susceptible to the effect and treatment with ivermectin may be deadly.
Long used in veterinary medicine, there were only limited trials of the drug on humans up until the 1980s. However, initial human trials were very promissing and Ivermectin quickly replaced many of the more toxic alternatives for parasite treatment. Now because of its safety in most humans, ivermectin can be given when parasites are even suspected without fear of adverse reaction.