Peptide Hormones: EPO Erythropoietin, also known as Epo, is a protein that is made by that kidney that stimulates the formation of red blood cells. Red blood cells carry oxygen in the blood and more red blood cells means better endurance performance. Erythropoietin alpha is sold as Epogen and Procrit and a synthetic form called darbepoetin is sold as Aranesp.
All of these products are produced in an injectable form. Aranesp is dosed weekly or every two weeks while Epogen is dosed three times per week. Dosing depends on the level of hemoglobin or hematocrit that is to be achieved. If hematocrit is elevated too much, the user runs the risk of heart attack or stroke due to increased blood thickness.
Some athletes use IV fluids at the same time to dilute the blood as well as to evade blood testing. Erythropoietin testing is still in its infancy and is unreliable however, if the hemoglobin or hematocrit level is too high, then it will be interpreted as doping.