I suspect drug usage is widespread, though I'd have no idea of exactly what is taken and by whom.
When there's money and fame at stake, some people will be unable to resist.
There was that American competition climber (correct me if I'm wrong here) that I heard about - he spent something like $30k on an operation to "disconnect" the sweat glands in his hands. Now, if people are willing to go to those sort of extremes, then I'm sure many will take drugs.
And let's not forget that it's part of Peak climbing folklore that certain of our UK heroes used to train using amphetamines.