Parasites are organisms larger than yeast or bacteria that can cause infection, usually in the intestines. The most common parasites to infect humans in the United States and Canada are giardia (Giardia lamblia), Entamoeba histolytica, cryptosporidium (Cryptosporidium spp.), roundworm (Ascaris lumbricoides), hookworm (Ancylostoma duodenale and Necator americanus), pinworm (Enterobius vermicularis), and tapeworm (Taenia spp.).

Infection with parasites can be life-threatening in people with severe impairment of immune function. People should consult a physician if they suspect a parasitic infection.

Caution: Any herb potent enough to kill parasites could potentially harm the person taking it. Although some herbs have antiparasitic actions in test tubes, none has been adequately tested for efficacy or safety in humans. Safe and proper use requires the skills of an experienced practitioner.