Joke about cocaine? (5)
I believe the answer is:
crack
This clue is a double definition.
'joke' is the first definition.
(thesaurus)
'cocaine?' is the second definition.
(crack is a kind of cocaine)
'about' is the link.
(Other definitions for crack that I've seen before include "Work out" , "Joke; split" , "Drug - solve" , "Opening; sharp blow" , "Ace" .)