A Very Valuable Quote From FTS10

"All things are poison and nothing is without poison, only the dose permits something not to be poisonous."
-Philippus Theophrastus Aureolus Bombastus von Hohenheim (Paracelsus)

I distinctly remember that the difference between a poison and a parasite medicine is that the medicine is a small enough dosage to only kill the invading organisms. If the dosage was upped it would kill the infected organism.
This lesson I learned from Bob is grade school when he was teaching us about getting rid of parasites in a fishtank.