Lance Armstrong used banned drug EPO, ex-teammate says: What's EPO?

(CBS/AP) Lance Armstrong cheated. At least that's the allegation made by one of his former teammates, who says the seven-time Tour de France champion injected himself with the prohibited blood-boosting substance EPO (erythropoietin) before and during races.

The teammate, Tyler Hamilton, told CBS News "60 Minutes" that Armstrong had used EPO when competing in the 1999 Tour de France and while preparing to compete in the 2000 and 2001 Tours.

"I saw [EPO] in his refrigerator," Hamilton told "60 Minutes" correspondent Scott Pelley. "I saw him inject it more than one time, like we all did, like I did, many, many times."

Armstrong denied the allegation, launching a website to tell his side of the story. He also tweeted: "20+ year career. 500 drug controls worldwide, in and out of competition. Never a failed test. I rest my case."

Whatever the truth about Hamilton's allegations, there's no doubt that EPO can give a major boost to an athlete's performance.

A synthetic hormone, EPO was developed for treating the lack of red blood cells that comes with kidney disease, HIV/AIDS, and cancer, according to the website of the National Strength and Conditioning Association. It works by stimulting the body to produce more red blood cells, thereby boosting the amount of oxygen that gets to exercising muscles.

EPO can be taken intravenously or by injection under the skin. The most common side effect seems to be an increase in blood pressure, according to the association's website. Suspected misuse of EPO is suspected in the deaths of 19 Dutch and Belgian cyclists between 1987 and 1990.

The U.S. Anti-Doping Agency has more on EPO and other performance-enhancing drugs.