A new drink gives a hearty complaint (6)
I believe the answer is:
angina
'hearty complaint' is the definition.
(complaint of the heart)
'a new drink gives a' is the wordplay.
'a' becomes 'an'.
'new drink gives' becomes 'gin' (I can't justify this - if you can you should believe this answer much more).
'an'+'gin'+'a'='ANGINA'
Can you help me to learn more?
(Other definitions for angina that I've seen before include "Sharp chest pain caused by heart disease" , "chest complaint" , "heartfelt complaint?" , "Painful heart complaint." , "Painful heart condition" .)