Whistle-blower concerned with liberal swallowing ecstasy (7)
I believe the answer is:
referee
'whistle-blower' is the definition.
'concerned with liberal swallowing ecstasy' is the wordplay.
'concerned with' becomes 're'.
'liberal' becomes 'free' (I've seen this before**).
'swallowing' indicates putting letters inside.
'ecstasy' becomes 'e' (informal term for the drug).
'free' enclosing 'e' is 'feree'.
're'+'feree'='REFEREE'
(Other definitions for referee that I've seen before include "Arbiter" , "Sports official" , "Judge" , "Sports adjudicator" , "One who decides" .)