Mr Armstrong was a seven time Tour de France winner between 1999 and 2005, but was stripped of his titles in 2012, and admitted to using performance enhancing drugs in 2013.
The former cyclist was diagnosed with cancer in 1996, at the age of 25, but was declared cancer free a year later, and went on to win seven consecutive titles with the help of performance enhancing drugs.
During an interview for a new documentary, titled Lance, made for the 30th anniversary of ESPN, Mr Armstrong admitted that he took performance enhancing drugs from the age of 21, and had doped before he had even won a major event.
In the documentary, filmmaker Marina Zenovich asked him if he took any other supplements or injections before he started doping.
“Yes. But they weren’t illegal, so that… You know…” Mr Armstrong replied.
The filmmakers then asked the 48-year-old if he knew what he was injecting into his body as part of the doping.
“Of course. Oh, yeah, yeah, yeah. Come on,” he replied. “I’m not one of those guys. I was always, ‘Ooh — what do we have here?” I always asked, and I always knew, and I always made the decision on my own. Nobody said, “Don’t ask; this is what you’re getting.’”
He added: “I never, ever would have gone for that. I educated myself on what was being given, and I chose to do it.”
According to the Daily Mail, in another clip Mr Armstrong is then asked by the documentary team if he thinks taking performance enhancing drugs caused his testicular cancer.
“You know, I don’t know the answer to that. I don’t want to say no, because I don’t think that’s right either. I don’t know if it’s yes or no, but I certainly wouldn’t say no,” he said.
“The only thing I will tell you is, the only time in my life that I ever did growth hormone was the 1996 season,” Mr Armstrong added.
“And so just in my head, I’m like, growth… growing hormones and cells, like… if anything good needs to be grown, it does. But wouldn’t it also make sense that if anything bad is there, that it too would grow?”
Lance airs its first episode on 24 May on ESPN and concludes a week later on 31 May.