Caffeine, maybe it's lifting briefly Scottish island worker (9)
I believe the answer is:
stimulant
'caffeine' is the definition.
(thesaurus)
'it's lifting briefly scottish island worker' is the wordplay.
'lifting' is a reversal indicator.
'briefly' means to remove the last letter.
'scottish island' becomes 'mull' (Isle of Mull).
'worker' becomes 'ant' (worker is a type of ant).
'its' back-to-front is 'sti'.
'mull' with its last letter taken off is 'mul'.
'sti'+'mul'+'ant'='STIMULANT'
'maybe' acts as a link.
(Other definitions for stimulant that I've seen before include "Energizer" , "Something promoting activity" , "Something that promotes activity" , "Increasing vital action" , "Reviver" .)