A non-drinker, pain, embassy worker (7)
I believe the answer is:
attache
'embassy worker' is the definition.
(I've seen this in another clue)
'a non-drinker pain' is the wordplay.
'non drinker' becomes 'tt' (abbreviation for teetotaller).
'pain' becomes 'ache' (ache is a kind of pain).
'a'+'tt'+'ache'='ATTACHE'
(Other definitions for attache that I've seen before include "Military assistant" , "Specialised envoy" , "Small rectangular document case" , "This case is for carrying documents" , "Ambassador's aide" .)