Drug addicts consuming heroin are escorts (6)
I believe the answer is:
ushers
'are escorts' is the definition.
(I've seen this before)
'drug addicts consuming heroin' is the wordplay.
'drug addicts' becomes 'users' (I've seen this before).
'consuming' is an insertion indicator.
'heroin' becomes 'h' (synonyms).
'users' placed around 'h' is 'USHERS'.
(Other definitions for ushers that I've seen before include "Rushes with conductors" , "Escorts" , "They show attendees to seats" , "They show people to their seats in theatres" , "Theatre attendants" .)