Thiamine isn’t a bad treatment for allergies (13)

I believe the answer is:

antihistamine

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'treatment for allergies' is the definition.
I can't tell whether this defines the answer.

'thiamine isn't a bad' is the wordplay.
'bad' indicates anagramming the letters.
'thiamine'+'isnt'+'a'='thiamineisnta'
'thiamineisnta' with letters rearranged gives 'ANTIHISTAMINE'.

Can you help me to learn more?

(Other definitions for antihistamine that I've seen before include "Hay fever treatment" , "Medicine used to treat allergies" , "Allergy drug" , "Drug treating allergies" .)

I've seen this clue in The Times.

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