Drug work I polished off (6)
I believe the answer is:
opiate
'drug' is the definition.
(opiate is a kind of drug)
'work i polished off' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'polished off' becomes 'ate' (I've seen this in other clues).
'op'+'i'+'ate'='OPIATE'
(Other definitions for opiate that I've seen before include "Poppy-derived drug" , "something stupefying" , "Poppy-based drug" , "Does it ease pain" , "Drug made from poppy" .)