Shrink cured loony with drug (6)
I believe the answer is:
reduce
'shrink' is the definition.
(reducing is a kind of shrinking)
'cured loony with drug' is the wordplay.
'loony with' is an anagram indicator.
'drug' becomes 'e' (e is another name for ecstasy).
'cured' anagrammed with 'e' can make 'REDUCE'.
(Other definitions for reduce that I've seen before include "Subjugate; make (sauce) thicker" , "diet" , "Cut down, lose weight" , "Cut down on,lessen" , "'Cut down, abridge (6)'" .)