Insane psychopath arose where chemist’s seen (11,4)

I believe the answer is:

apothecarys shop

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'insane psychopath arose' is the definition.
I can't judge whether this definition defines the answer.

'chemist's seen' is the wordplay.
'chemist's' becomes 'apothecary's' ('apothecary' can be a synonym of 'chemist').
'seen' becomes 'shop' (I can't explain this - if you can you should believe this answer much more).
'apothecarys'+'shop'='APOTHECARYS SHOP'

'where' acts as a link.

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I've seen this clue in The Guardian.

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