Stepanova secretly recorded Russian coaches and athletes describing how they used performance-enhancing drugs - evidence used to ban more than 100 Russian athletes from the Olympics this year.
She has been called a traitor by her former coach Vladimir Kazarin and is currently in hiding in North America with her husband Vitaly, a former Russian anti-doping official.
"In 2007, for the first time my coach (Kazarin) started giving me testosterone injections," she told the BBC in an interview.
"I did know it was banned, but before giving it to me I think my coach prepared me well because he was telling me stories about how it's normal, that's how it's done.
"Every night I had a dream that the doping inspectors were coming to test us, every single night the same nightmare. I was really afraid of being tested because I didn't know how the system worked.
"I didn't realise that the management was in on it, that even if you're caught you won't be disqualified if your coach has connections."
Stepanova, who was given a two-year ban in 2013 for abnormalities in her blood passport, said that suspension made her determined to expose how deep the problems in Russian athletics had actually spread.
