[jey]

No, it's primarily an adenosine antagonist.

http://en.wikipedia.org/wiki/Caffeine#Mechanism_of_action

[derefr]

Right, that's why I said "effectively": caffeine inhibits adenosine from inhibiting cholinesterase (which itself inhibits acetylcholine.) Isn't biology fun?

[jey]

That may be true, but the difference is that caffeine doesn't inhibit cholinesterase across the board.