[kristo]

I was a cyclist and my brother is now a professional. It's rare. There was a time when it was rampant and accepted. Then a time when it was not accepted but prevalent as the controls lagged severely behind the methods (Lance Armstrong). As controls have developed and the risk of detection has grown, it has become much more rare.

[nwienert]

This is a "trust me bro" reply though, there are constant developments in research chemicals that aren't easily detected. I know a top-20 boxer who thinks doping is common it's just harder to detect now.

Perhaps at lower levels, but at the highest levels it seems impossible to prove the negative.