A stimulant, but no starter for meal (5)
I believe the answer is:
upper
'a stimulant' is the definition.
(I've seen this before)
'no starter for meal' is the wordplay.
'no starter for' means to remove the first letter.
'meal' becomes 'supper' (supper is a kind of meal).
'supper' with its initial letter removed is 'UPPER'.
'but' is the link.
(Other definitions for upper that I've seen before include "Higher in place or position" , "Stimulant drug (informal)" , "Higher; part of shoe" , "Part of a shoe; drug" , "Pep pill" .)