Nag coke and heroin overwhelm imaginative skill (9)
I believe the answer is:
carthorse
'nag' is the definition.
(I know that carthorse is a type of nag)
'coke and heroin overwhelm imaginative skill' is the wordplay.
I cannot quite see how this works, but
'coke' could be 'c' (synonyms) and 'c' is present in the answer.
'heroin' could be 'horse' (slang term for heroin) and 'horse' is present in the answer.
'skill' could be 'art' (both can mean a talent) and 'art' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for carthorse that I've seen before include "large drawer" , "Equine" , "has pulling power" , "Beast of burden" .)