Coffee or endless tea for the medical officer (5)
I believe the answer is:
mocha
'coffee' is the definition.
(type of coffee drink)
'endless tea for the medical officer' is the wordplay.
'endless' means to remove the last letter.
'tea' becomes 'char' (I've seen this before).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'the medical officer' becomes 'MO' (abbreviation).
'char' with its final letter taken away is 'cha'.
'cha' after 'mo' is 'MOCHA'.
'or' acts as a link.
(Other definitions for mocha that I've seen before include "Yemeni port; type of coffee bean" , "Deep brown; a fine coffee" , "Kind of coffee" , "Macho (anag.); coffee with chocolate" , "It may end up as grounds" .)