American cyclist Lance Armstrong has admitted taking banned substances, including blood-boosting agent EPO, to help win the Tour de France.

After years of denials, the 41-year-old told talk show host Oprah Winfrey that he doped during his cycling career.

In an explosive start to the much-anticipated interview, Armstrong confirmed he doped during all seven of his Tour de France wins, from 1999 to 2005, and admitted he used EPO. He also conceded he "blood doped", used blood transfusions and took banned substances like testosterone, cortisone and human growth hormone.

Armstrong told Winfrey that at the time of his drug-taking it did not feel wrong, he did not feel bad about it and that he did not feel it was cheating, as he was creating a level playing field with other riders who took drugs - but he said he had now changed his opinion.

And he added: "I'll spend the rest of my life trying to earn back trust and trying to apologise to people. For the rest of my life. I see the anger in people. And betrayal. It's all there. These are people that supported me, believed in me. They have every right to feel betrayed. And it's my fault. I will spend the rest of my life trying to earn back trust and apologise to people."

Armstrong said he believed that doping was necessary to win the Tour de France. He said: "That's like saying we have to have air in our tyres or water in our bottles. It was part of the job. I don't want to make any excuses, but that was my view and I made those decisions."

Armstrong insisted it was his successful battle with testicular cancer, chronicled in his books and which prompted the establishment of the Livestrong charity, which increased his desire to win at all costs.

The Texan, who was stripped of his seven Tour de France titles and his Olympic bronze medal from Sydney in 2000, was banned for life after the United States Anti-Doping Agency (USADA) found him to be a central figure in "the most sophisticated, professionalised and successful doping programme that sport has ever seen".

But Armstrong denied this was the case, saying: "It wasn't. It was definitely professional and it was definitely smart, if you can call it that. But it was very conservative, very risk averse."

In the interview, recorded on Monday in his home town of Austin, Texas, Armstrong was asked why he had waited until now to admit his misdemeanours. He said: "I don't know that I have a great answer. This is too late. It's too late for probably most people and that's my fault. I view this situation as one big lie, that I repeated a lot of times. It wasn't as if I just said no."