Friend taking Ecstasy in passage (5)
I believe the answer is:
alley
'passage' is the definition.
(thesaurus)
'friend taking ecstasy' is the wordplay.
'friend' becomes 'ally' (I've seen this before).
'taking' is an insertion indicator.
'ecstasy' becomes 'e' (informal term for the drug).
'ally' going around 'e' is 'ALLEY'.
'in' acts as a link.
(Other definitions for alley that I've seen before include "space in US court" , "Passage between houses, perhaps" , "Back lane" , "Narrow back street" , "Bowling lane" .)