Crossword Genius

Plant two drugs (9)

Ross

I believe the answer is:

horseweed

'plant' is the definition.
(horseweed is a kind of plant)

'two drugs' is the wordplay.
'two drugs' can mean two substitutions for 'drug'.
'drug' becomes 'horse' (horse is a slang term for heroin).
'drug' becomes 'weed' (weed is a kind of drug).
'horse'+'weed'='HORSEWEED'

I've seen this clue in The Guardian.
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