Young man smuggling ecstasy for Guide (4)
I believe the answer is:
lead
'for guide' is the definition.
(lead can mean to usher or guide)
'young man smuggling ecstasy' is the wordplay.
'young man' becomes 'lad' (lad can mean a boy or young man).
'smuggling' is an insertion indicator (some letters smuggled inside).
'ecstasy' becomes 'E' (informal term for the drug).
'lad' going around 'e' is 'LEAD'.
(Other definitions for lead that I've seen before include "Short wire used as jumper - Pb" , "Metal; clue" , "Guide, conduct" , "Chemical element, symbol Pb" , "Guide, direct" .)