Beat the booze, but not ecstasy (5)
I believe the answer is:
thrum
'beat' is the definition.
('thrum' can be a synonym of 'beat')
'the booze but not ecstasy' is the wordplay.
'booze' becomes 'rum' (rum is a kind of booze).
'but not' is a deletion indicator.
'ecstasy' becomes 'e' (informal term for the drug).
'the'+'rum'='therum'
'therum' with 'e' removed is 'THRUM'.
(Other definitions for thrum that I've seen before include "Drone; tap idly" , "Make a rhythmic humming sound" , "Drum incessantly" , "Rhythmic buzzing sound - fringe left after weaving" , "go on and on" .)