Cocaine's about acceptable before Ecstasy (4)
I believe the answer is:
coke
'cocaine's' is the definition.
('coke' can be a synonym of 'cocaine')
'about acceptable before ecstasy' is the wordplay.
'about' becomes 'c' (abbreviation for 'circa'**).
'acceptable' becomes 'ok'.
'before' is a charade indicator (letters next to each other).
'ecstasy' becomes 'e' (informal term for the drug).
'c'+'ok'+'e'='COKE'
(Other definitions for coke that I've seen before include "Fuel made from coal" , "Substance left after gas and tar have been extracted from coal" , "Drink - drug - solid-fuel product" , "something for heating" , "Furnace fuel" .)