Dwain Chambers claims there will always be athletes using performance-enhancing drugs because the scientists will remain one step ahead of the testers.
Chambers was fifth in last year's European 100m final
The former European 100m champion served a two-year ban for taking the designer steroid THG in 2003.
"It's simple, science always moves faster than the testers.
"Some people take chances, some don't, and I was willing to take that chance," he said in an interview with the BBC's Inside Sport programme.
"I was under the assumption that I wouldn't get caught."
When asked whether a clean athlete was likely to beat one using drugs in an Olympic final, Chambers added: "It's possible, but the person that's taken drugs has to be having a real bad day. That's what I believe."
Chambers returned to competition last year and was part of the victorious British 4x100m team at the European Championships in Gothenburg, while finishing fifth in the individual final.
But he has decided to switch to American football for financial reasons and is currently embarking on a career in NFL Europa with the Hamburg Sea Devils.
"We all go through different chapters in life," he said.
"I came to a crossroad in my life where I took a wrong turn, you know, got hit by a bus
"But fortunately I was able to get back up on my feet and you know, go in another direction."