Bitter alkaloid used in tonic water (7)

I believe the answer is:

quinine

(Other definitions for quinine that I've seen before include "Medicinal substance from cinchona bark" , "Tonic flavouring" , "Antimalarial ingredient of 9" , "Bitter compound used as a tonic" , "Fever-reducing drug" .)

I've seen this clue in The Guardian.

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