BOB DOUGHTY: One method of doping is called blood doping. It is the use of substances like hormones or even blood itself to increase production of red blood cells. That way, the blood moves more oxygen to the muscles, increasing their strength. One such hormone is EPO. It is said to be most-useful to athletes in endurance sports such as cycling and distance-running. Yet doctors say hormones used for blood doping thicken the blood and increase the chances of heart disease or stroke. And the use of blood from another person can spread viruses. But doctors say even the use of a person’s own blood to increase the level of red blood cells can raise the risk of heart disease and stroke.

Another substance that can improve performance is human growth hormone, or HGH. This hormone is produced naturally by the pituitary gland in the brain. Experts say higher than normal levels of the human growth hormone can cause diabetes, muscle and bone pain, high blood pressure or other disorders.

FAITH LAPIDUS: The White House Office of National Drug Control Policy provided a statement about sports doping to VOA. The office said it understands that athletes have a powerful effect on young people. The Office of National Drug Control Policy said it works closely with anti-doping agencies in the United States and other countries. And it attempts to influence sports organizations throughout the world to create policies to fight the use of performance-enhancing drugs.