Expert in wordplay and drug-free diet (6)
I believe the answer is:
pundit
'expert' is the definition.
(I've seen this before)
'wordplay and drug-free diet' is the wordplay.
'wordplay' becomes 'pun' (synonyms).
'and' is a charade indicator (letters next to each other).
'drug' becomes 'e' (e is another name for ecstasy).
'free' is a deletion indicator.
'diet' with 'e' taken out is 'dit'.
'pun'+'dit'='PUNDIT'
'in' is the link.
(Other definitions for pundit that I've seen before include "Maestro" , "Talking expert" , "Expert (sometimes self-appointed)" , "A person of great learning" , "An expert or critic in a particular field" .)