Are after dog poison? (6)
I believe the answer is:
curare
'poison?' is the definition.
(I know that curare is a type of phytotoxin)
'are after dog' is the wordplay.
'after' is a charade indicator (letters next to each other).
'dog' becomes 'cur' (both can mean a despicable person).
'are' put after 'cur' is 'CURARE'.
(Other definitions for curare that I've seen before include "Poison used on darts" , "Paralysing plant poison" , "Poison applied to darts" , "Arrow poison" , "Poison put on arrows" .)