Note something that is supposed to make you feel better (5)
I believe the answer is:
tonic
This clue is a double definition.
'note' is the first definition.
(type of note in a musical scale)
'something that is supposed to make you feel better' is the second definition.
(substance taken to stimulate oneself)
(Other definitions for tonic that I've seen before include "requirement for invigoration?" , "A pick-me-up drink, nice with gin" , "do for musicians" , "An enlivener" , "something medicinal" .)