Armstrong passed more than 500 drug tests during his career. In some cases, however, he was found to have used substances, including EPO, years after he retired when new tests could find previously untraceable drugs.
However, he denied a claim by former teammate Floyd Landis that he organized a cover-up and paid off officials when, in 2001, he allegedly failed a test prior to the Tour de Suisse.
Armstrong used his wealth and influence to go after any of his teammates or crew members who attempted to expose him. He sued a team masseuse and as well former teammate Frankie Andreu and his wife, Betsy Andreu, who claimed to have overheard Armstrong telling a doctor that he used multiple banned substances.
Armstrong said he believed he would not have been caught had he not come out of retirement in 2008, just after former teammate Floyd Landis was caught doping and stripped of the 2006 Tour de France title.
He said, however, that his "fate was sealed" when George Hincapie, the only teammate with whom he competed in all seven winning Tours de France, was forced to testify against him to USADA.
Minutes after the interview concluded, Livestrong – the cancer foundation that he founded – released a statement expressing disappointment in their former leader.
"We at the LIVESTRONG Foundation are disappointed by the news that Lance Armstrong misled people during and after his cycling career, including us. Earlier this week, Lance apologized to our staff and we accepted his apology in order to move on and chart a strong, independent course," the statement read.
"Our success has never been based on one person ¬it's based on the patients and survivors we serve every day, who approach a cancer diagnosis with hope, courage and perseverance."
Also on Thursday, before the Winfrey interview aired, the International Olympic Committee stripped Armstrong of his 2000 Olympic bronze medal.