Futile advice to junkie? (7)

I believe the answer is:

useless

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'futile' is the definition.
(similar in meaning)

I don't understand how the rest of the clue works.

(Other definitions for useless that I've seen before include "Counterproductive" , "Is Sue less impractical?" , "Not worth a jot" , "Lacking in purpose" , "nohoper?" .)

I've seen this clue in The Guardian.

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