Carry drug in pub (4)
I believe the answer is:
bear
'carry' is the definition.
(bear can mean to transport or carry)
'drug in pub' is the wordplay.
'drug' becomes 'e' (E is another name for ecstasy).
'in' indicates putting letters inside.
'pub' becomes 'bar' (both are drinking establishments).
'e' going into 'bar' is 'BEAR'.
(Other definitions for bear that I've seen before include "Give birth to - large mammal" , "Exhibit" , "stomach and > suffer" , "Endure - mammal" , "stand" .)