Fancy drink containing drug (5)
I believe the answer is:
dream
'fancy' is the definition.
(both can mean a fantasy)
'drink containing drug' is the wordplay.
'drink' becomes 'dram' (small alcoholic drink).
'containing' is an insertion indicator.
'drug' becomes 'e' (E is another name for ecstasy).
'dram' going around 'e' is 'DREAM'.
(Other definitions for dream that I've seen before include "King had one" , "Bedroom vision?" , "Sleeper's vision" , "Part of sleep" , "Night-time fantasy" .)