One maybe giving drug in city to junior nurses (8)

I believe the answer is:

injector

'one maybe giving drug' is the definition.
(someone injecting a drug)

'in city to junior nurses' is the wordplay.
'city' becomes 'EC' (the City of London postcode).
'junior' becomes 'Jr' (abbreviation).
'nurses' indicates putting letters inside (nurse can mean to hold onto or harbour).
'ec'+'to'='ecto'
'ecto' put within 'jr' is 'jector'.
'in'+'jector'='INJECTOR'

(Another definition for injector that I've seen is " Needle".)

I've seen this clue in The Times.

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