The sport of cycling, if it’s possible, just got a little dirtier on Thursday. Tyler Hamilton, a former teammate of seven-time Tour de France champion Lance Armstrong, revealed that Armstrong injected himself with the prohibited blood-boosting substance EPO before and during races.

Hamilton, whose full comments will be shown Sunday night on CBS’ “60 Minutes,” said that Armstrong had used EPO when competing in the 1999 Tour de France and while preparing to compete in the 2000 and 2001 Tours.

Armstrong “took what we all took … the majority of the peloton,” Hamilton told CBS reporter Scott Pelley. “There was EPO … testosterone … a blood transfusion.”

EPO can be taken intravenously or by injection under the skin. It works by stimulating the body to produce more red blood cells, thereby boosting the amount of oxygen that gets to exercising muscles.

Because blood doping is so prevalent in cycling, Armstrong has long been accused of doping but has always denied it and never has tested positive. Armstrong responded to this 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.” Armstrong’s attorney Mark Fabiani said: “Tyler Hamilton is a confessed liar in search of a book deal — and he managed to dupe ’60 Minutes.’ ”

Armstrong, 39, abruptly retired in January after the Tour Down Under in Australia. He is the target of a federal investigation into use of illegal drugs that aid performance. Hamilton, like previous Armstrong accuser Floyd Landis, has been suspended for doping – he was suspended from the tour between 2005 and ’07, and retired after failing another test in ’09. His first official failed drug test came in 2004, at the Spanish Vuelta, only six weeks after he won his Olympic gold medal and a year after he won a stage at the 2003 Tour de France.

Two former teammates of Armstrong said Friday they never saw Armstrong use banned drugs. The European pair also said they weren’t particularly close to the American riders and weren’t in the “inner circle” like Hamilton was.

The International Olympic Committee could strip Hamilton of his 2004 gold medal following Hamilton’s admission of doping, IOC vice president Thomas Bach said Friday. The IOC can retroactively strip Olympic medals if proof of doping emerges later or an athlete admits to cheating. The IOC took away Marion Jones’ five medals from the 2000 Sydney Games after she admitted using performance-enhancing drugs.

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