Crack supply (not ecstasy) (4)
I believe the answer is:
note
'crack' is the definition.
(thesaurus)
'not ecstasy' is the wordplay.
'ecstasy' becomes 'E' (informal term for the drug).
'not'+'e'='NOTE'
'supply' acts as a link.
(Other definitions for note that I've seen before include "Tone of distinction" , "Memo; piano key" , "Memo - sound - fame" , "mention" , "Record; memo" .)