Armstrong's biggest rival, German Jan Ullrich, three times second to the seven-times winner, was found guilty last year of being involved in the Operation Puerto blood-doping scandal which broke in 2006.
Italian Ivan Basso, second in 2005 and third in 2004, was also implicated in the scandal, and Swiss Alex Zuelle, second in 1999, admitted taking EPO the previous year.
Armstrong, in a confessional interview with American chat-show host Oprah Winfrey shown on Thursday, said there was a culture of drugs in cycling that made for a "level playing field."
When he won his first Tour de France, the sport was reeling from the 1998 Festina doping scandal after the team's manager Bruno Roussel had confessed to the existence of "an organised doping system".
Organisers, riders and pundits were quick to dub the 1999 race the "Tour of renewal".
Armstrong, however, said there had been no out-of-competition testing and that the EPO test had not yet been enforced, making it easier for everyone to cheat.
Doping was endemic in the early 2000s and there is no way that could be denied, Armstrong's former team mate Tyler Hamilton, who gave back his 2004 Olympic gold medal after confessing to doping throughout his career, told Reuters last year.
"They have to bury their heads in the sand, literally - which is impossible," he said.
Doping did not stop after Armstrong first retired in 2005, with cycling being hit hard in 2006 by the Puerto scandal and by Floyd Landis's positive test for testosterone while winning the Tour that year.
In 2007, Dane Michael Rasmussen was kicked off the Tour by his team while leading the overall standings for lying about his whereabouts - information required under anti-doping regulations.
The following year, several riders, including third-placed Bernhard Kohl, retroactively tested positive for the banned blood-booster EPO-CERA.
Some riders, however, spoke out against drugs even in the darkest hours of the sport.
Frenchman Christophe Bassons left the Tour in 1999, saying he had been bullied by Armstrong because he was writing a daily column about doping in a French newspaper.
"At the time, I had the best test results in my whole team," Bassons was quoted as saying in French media. "I wanted to show that you could do it without doping."
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