Handle fellow turning to drug (4)
I believe the answer is:
name
'handle' is the definition.
(thesaurus)
'fellow turning to drug' is the wordplay.
'fellow' becomes 'man' (I've seen this before**).
'turning' shows that the letters should be reversed in order.
'to drug' becomes 'e' (e is another name for ecstasy).
'man' reversed gives 'nam'.
'nam'+'e'='NAME'
(Other definitions for name that I've seen before include "Title, term" , "By which a person is known" , "Identification" , "Monicker" , "By which one is known" .)