Marion Jones was another famous case of doping. She was an athlete competing sprints and long jump. She won 3 gold medals and 3 bronze medals at the 2000 Olympic Games in Sidney.
Seven years later, after and exhaustive doping investigation, she confessed had taken banned substances, steroids in that case, in the Olympic Games. Because of it, she was forced to return her 5 medals and was disqualified for two years.
One of the more used illegal substances is EPO. It increases the red blood cell production, what improve the physical performance. But it could have very dangerous side effects due to the thickening of the blood, EPO can cause strokes and heart attacks. One of the sports where have been more cases of this kind of doping is cycling.