Drug category that's uncommon (5,5)

I believe the answer is:

upper class

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'that's uncommon' is the definition.
I can't judge whether this defines the answer.

'drug category' is the wordplay.
'drug' becomes 'upper' (a type of stimulating drug).
'category' becomes 'class' (synonyms).
'upper'+'class'='UPPER-CLASS'

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(Other definitions for upper class that I've seen before include "Posh" , "Aristocratic" , "Top social echelon" .)

I've seen this clue in The Irish Times.

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