Instruction to give ‘em tonic? (4-2-2)
I believe the answer is:
pick-me-up
But I can't explain it at all!
(Other definitions for pick-me-up that I've seen before include "A tonic to restore health or relieve depression" , "Stimulative drink" , "Stimulant" , "I could do with a lift" , "Stimulating drink" .)