Drug's fixed (8)

I believe the answer is:

specific

I believe this is a double definition.

'drug's' is the first definition.
(specific is a kind of drug)

'fixed' is the second definition.
(thesaurus)

(Other definitions for specific that I've seen before include "Old medicine" , "Particular, special" , "Peculiar" , "Particular, definite" , "Precise, clearly defined" .)

I've seen this clue in The Telegraph.

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