Picker-upper (5)
I believe the answer is:
tonic
'picker-upper' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tonic that I've seen before include "Key" , "shot in the arm" , "A pick-me-up drink, nice with gin" , "Carbonated mixer" , "Producing tension of muscles" .)