Carry drug into pub (4)
I believe the answer is:
bear
'carry' is the definition.
(bearing is a kind of carrying)
'drug into pub' is the wordplay.
'drug' becomes 'e' (e is another name for ecstasy).
'into' means one lot of letters goes inside another.
'pub' becomes 'bar' (I've seen this before).
'e' placed inside 'bar' is 'BEAR'.
(Other definitions for bear that I've seen before include "Carry; large mammal" , "a churlish individual" , "Show" , "Massive mammal" , "It could be polar or grizzly" .)