After inhaling drug, pass on joint (6)
I believe the answer is:
reefer
'joint' is the definition.
(informal term for a marijuana joint)
'after inhaling drug pass on' is the wordplay.
'after inhaling' is an insertion indicator.
'drug' becomes 'e' (E is another name for ecstasy).
'pass on' becomes 'refer' (to refer someone elsewhere is to pass them on).
'e' inserted inside 'refer' is 'REEFER'.
(Other definitions for reefer that I've seen before include "drugged cigarette" , "Jacket for a sailor" , "Kind of jacket - joint" , "pot holder?" , "Jack < 's joint" .)