I second the conclusions of Wahine's discussion. I had a similar one at work (no health care experts present, but a few cycling fans). I enjoy watching cycling, but the doping is present at every level, not just professionals. Yesterday there was news of 2 amateur cyclists doping for the NY Gran Fondo (see Bike Radar).

I think seeking surges in performance is probably like any addictive behavior: some people may try it once and really long for the performance boost. That, to me, would explain why amateurs do it, too.