Human performance is complicated, and there can certainly be placebo effects as well as competition effects. And, some riders will do anything they think will get them a leg up on the competition.

The "micro dosing" that was in the news a while ago may well be a placebo effect.

But, for the regular increase HCT by EPO, Blood Transfusions, etc, the theory is strong, and appears to be borne out by actual on the road testing.

These are extraordinary athletes with or without drugs. But, perhaps just a little better with drugs.