EPO is a performance-enhancing drug that stimulates red blood cell creation, increasing oxygen levels in the body. It allows athletes in endurance sports like cycling and running to maintain steady breathing and not slow down or stop during long distance events. While originally developed to treat medical conditions causing anemia, athletes use EPO to enhance performance and chances of winning. However, EPO is dangerous as it raises hematocrit levels, thickening the blood and risking strokes, heart attacks, and clogged capillaries.