Erythropoietin (pronunciation: [ɪˈɹɪθ.ɹoˌpo.ɪ.tɪn], synonyms: EPO, Erythropoetin, and Epoetin--a synthetic version) is a hormone produced by the kidneys. It makes more red blood cells grow. It is used to treat anemia. Anemia can come from kidney failure or from chemotherapy to fix cancer. The man-made hormone is made with cell cultures. The hormone is also used for blood doping in endurance sports although this is illegal in all athletic competitions.