All eyes are on the Thursday, Jan 17 airing of Oprah Winfrey's show featuring the admission of cyclist Lance Armstrong that he used performance-enhancing drugs.

While Armstrong is not the first athlete accused of doping to enhance their performance, cyclists are among those who are frequently investigated for doping and research revealed that most of them, including Armstrong, were found or accused of using a particular drug - erythropoletin.

Erythropoletin is a glycoprotein hormone that controls red blood cell production. It is also called hematopoletin or hemopoletin and is produced by interstitial fibroblasts in the kidney. When used as a performance-enhancing drug, it s classified as an erythropolesis-stimulating agent (ESA).

ESA is often use as a blood doping agent by athletes in endurance sports such as cycling, horseracing, boxing, rowing, distance running, race walking, cross-country skiing, biathlon and triathlons. Sportsmen use ESAs to improve oxygen delivery to muscles, which directly improve their endurance capacity.

Though ESA was suspected to be widely used by athletes in the 1990s in some sports, it was only in 2000 that the French national anti-doping laboratory developed a direct test and was used for the first time in 2002 at the Winter Olympic Games in Salt Lake City.

In 2012, the U.S. Postal Service cycling team released the result of its probe that the team members, which include Armstong, used a cocktail of performance-enhancing substances to ensure their win in Tour de France 1999. As a consequence, Armstrong, a testicular cancer survivor, was stripped of his seven tour wins by USADA.

Besides Armstrong, here are 20 other cyclists who have been found to using ESA, admitted to taking it or suspended by a sporting body for failure to submit to a required drug testing.

1. Lizandro Ajcu - Guatemala

2. Peter Riis Andersen - Denmark

3. Frankie Andreu - U.S.

4. Mikel Astarloza - Spain

5. Niklas Axelsson - Sweden

6. Erwin Bakker - The Netherlands

7. Manuel Beltran - Spain

8. Udo Bolts - Germany

9. Laurent Brochard - France

10. Dave Bruylandts - Belgium

11. Oscar Camenzind - Switzerland

12. Joey D'Antoni - U.S.

13. Bert Dietz - Germany

14. Laurent Dufaux - Switzerland

15. Dario Frigo - Italy

16. Ivailo Gabrovski - Bulgaria

17. Philippe Gaumont - France

18. Fabrizio Guidi - Italy

19. Bo Hamburger - Denmark

20. Pascal Herve - France

Sports experts estimate that Armstrong stands to lose over $150 million in future commercial endorsements because of the doping charges. Among the many commercials that 41-year-old cyclist has done is that of Nike.

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