[Tuna-Fish]

Generally, never. Because any small change in chemistry is something that evolution is very effective at picking up. Which means that if there is a simple intervention that improves performance, there is always a good reason why nature hasn't already given it to you. In the case of EPO, it's significantly increased risk of blood clots and blood pressure related conditions.

[dr_dshiv]

Caffeine is still the only outlier?

I remain optimistic.

[sincerely]

Aspartame seems to be a newer contender