Erythropoietin, also known as EPO, is a hormone produced by the kidneys that stimulates the production of red blood cells. It is used as a medication to treat anemia caused by kidney disease, chemotherapy, and other medical conditions. Synonyms for erythropoietin include hematopoietin, erythropoiesis-stimulating agent, recombinant human erythropoietin, and alpha-erythropoietin. These terms are often used interchangeably and refer to the same medication. EPO has become a controversial substance in sports due to its ability to enhance athletic performance by increasing oxygen uptake and endurance. As a result, it is classified as a banned substance by the World Anti-Doping Agency.