Ecstasy smuggled in small deception (7)
I believe the answer is:
sleight
'deception' is the definition.
(I've seen this before)
'ecstasy smuggled in small' is the wordplay.
'ecstasy' becomes 'E' (informal term for the drug).
'smuggled in' indicates putting letters inside.
'small' becomes 'slight' (I've seen this in another clue).
'e' put within 'slight' is 'SLEIGHT'.
(Other definitions for sleight that I've seen before include "distraction?" , "Manual dexterity" , "Trickery" , "Hits leg (anag) - cunning" , "Dexterity (usually of hand)" .)