Armstrong was stripped of his seven Tour de France titles and banned for life as the US Anti-Doping Agency (USADA) released a scathing report in October last year, condemning him to be the centre of a "sophisticated" doping program while riding for the US Postal Service Team and Discovery Channel team between 1998-2005 in the Tour de France, reports Xinhua.
In the report, Armstrong was accused by about a dozen of former teammates of using performance-enchancing drugs and pressuring his teammates to do so.
When Winfrey asked Armstrong in the interview aired Thursday night whether these accusations were true, he admitted to it and said suffering from cancer had changed his attitude.
"I grew up as a fighter. Before my diagnosis, I was a competitor, but not so fierce," he said. When diagnosed with testicular cancer in 1996 he was given only a 40 percent chance of surviving. But survive he did, and he returned to cycling with a vengeance.
After that, Armstrong said, he wanted to win at all cost.
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In fighting cancer, the ruthless attitude was good, he said. But "that's bad" when he took it out in racing.
"I wasn't a bully before that," he said.