Crossword Genius

Not affected by a chemical substance (5)

Ross

I believe the answer is:

sober

(Other definitions for sober that I've seen before include "Far from drunk" , "Not intoxicated" , "Serious or solemn and not drunk" , "Serious; muted in colour" , "Sensible - clear-headed" .)

I've seen this clue in The Irish Times.
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