Private drug stash (7)
I believe the answer is:
secrete
'stash' is the definition.
(thesaurus)
'private drug' is the wordplay.
'private' becomes 'secret' ('secret' can be similar in meaning to 'private').
'drug' becomes 'e' (e is another name for ecstasy).
'secret'+'e'='SECRETE'
(Other definitions for secrete that I've seen before include "Hold and send out substance into the body as gland does" , "squirrel" , "harbour" , "(Of gland) produce (a substance)" , "Hide away" .)