Drunk back on hard stuff (4)
I believe the answer is:
tosh
'stuff' is the definition.
(both can mean nonsense)
'drunk back on hard' is the wordplay.
'drunk' becomes 'sot' ('sot' can be a synonym of 'drunk').
'back' says the letters should be written in reverse.
'on' is a charade indicator (letters next to each other).
'hard' becomes 'h'.
'sot' in reverse letter order is 'tos'.
'tos'+'h'='TOSH'
(Other definitions for tosh that I've seen before include "Slang nonsense" , "13 [TRIPE]" , "Humbug" , "Cobblers" , "Intimate" .)