Erythropoietin (EPO) – A natural hormone, used as a drug to improve an athlete's performance

(Pronounced ih-rith-roh-poi-ih-tn or ee-pee-oh)

Note: EPO is among the most well known methods of doping in sports. 

Thanks to her dog, the arithmetic she wrote out was ruined. There was no point handing it in (erythropoietin) after he'd peed over (EPO) it.

When the levels of oxygen levels go down, the production of erythropoietin goes up which stimulates the production of red blood cells to transport more oxygen. This is an adaptive system used by athletes at high altitude training who return to lower altitudes to compete with potentially more oxygen in the blood stream for 2 weeks. Some athletes bypass this all together by using erythropoietin or EPO doping which is considered cheating and an abuse of the rules. Professional athletes who take this are violating the anti-doping laws.