Consume couple of drugs outside bar (5)
I believe the answer is:
erode
'consume' is the definition.
(thesaurus)
'couple of drugs outside bar' is the wordplay.
'couple of' says to double the letters.
'drugs' becomes 'E' (somebody 'on E' could also be 'on drugs').
'outside' means one lot of letters goes inside another.
'bar' becomes 'rod' (I've seen this in other clues).
'e' duplicated is 'ee'.
'ee' enclosing 'rod' is 'ERODE'.
(Other definitions for erode that I've seen before include "Grind down" , "'Deteriorate, wear away (5)'" , "Slowly remove" , "fragment" , "Become ground down or deteriorate" .)