Coffee ingredient (8)
I believe the answer is:
caffeine
'coffee ingredient' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for caffeine that I've seen before include "Stimulant in tea, etc" , "Stimulant found in many beverages" , "The drug in coffee" , "Stimulant in drinks" , "Fine face (anag.)" .)