Hangover cure (4,2,3,3)
I believe the answer is:
hair of the dog
'hangover cure' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for hair of the dog that I've seen before include "may cover boxer" , "Maybe one in the morning" , "Alcohol as hangover cure (colloq.)" , "Morning tipple after night of excessive drinking" , "'...that bit one' completes a dubious hangover remedy" .)