Armstrong's revelation that he cheated in international cycling races acknowledges that he used a cocktail of performance-enhancing drugs to try to boost red blood cells, improve strength and stamina, and mask his cheating from anti-doping authorities.
Here are details of some of the drugs commonly used in sports doping.
* EPO is a peptide hormone that is produced naturally by the human body. It is released from the kidneys and acts on the bone marrow to stimulate red blood cell production. By injecting EPO, athletes aim to increase the concentration of red blood cells to boost their aerobic capacity.
* EPO abuse has serious health risks. By thickening the blood, EPO abuse can lead to an increased risk of heart disease, stroke and cerebral or pulmonary embolism. The drug has been implicated in the deaths of several athletes.
* There are two forms of blood doping. Autologous blood doping is the transfusion of an athlete's own blood, which has been stored, refrigerated or frozen, until needed. Homologous blood doping is the transfusion of blood taken from another person with the same blood type.
* Although the use of transfusions for blood doping dates back several decades, experts say it has seen a recent resurgence, probably due to the introduction of more efficient EPO detection methods.
* Anabolic steroids are drugs that resemble testosterone, a hormone produced in men's testes. Because these drugs affect muscle growth, raising their levels in the blood can help athletes to increase muscle size and strength. Athletes who use anabolic steroids also claim they reduce body fat and recovery time after injury.
* Examples of anabolic steroids include testosterone, stanozolol, boldenone, nandrolone and clostebol. Abuse of these drugs can make people aggressive and cause high blood pressure, liver problems, impotence and declining sperm production in men, kidney failure and heart disease.
HUMAN GROWTH HORMONE
* Human growth hormone (hGH)- also called somatotrophin or somatotrophic hormone - is naturally produced by the body and synthesised and secreted by cells in a gland at the base of the brain.
* The major role of hGH is to stimulate the liver and other tissues to secrete insulin-like growth factor IGF-1. IGF-1 stimulates production of cartilage cells, resulting in bone growth and also plays a key role in muscle and organ growth. All of these can boost sporting performance.
* Commonly reported side effects for hGH abuse are diabetes, worsening of heart diseases, muscle, joint and bone pain, high blood pressure, abnormal growth of organs and osteoarthritis.
* Diuretics can be used in a sport as a masking agent to prevent the detection of another banned substance. Examples of commonly used diuretics include furosemide, bendroflumethiazide and metolazone.
* As well as masking other drugs, diuretics can also help athletes lose weight, which they could use to their advantage in sports where they need to qualify in a certain weight category.