Stimulant blows head off drinker! (5)
I believe the answer is:
upper
'stimulant' is the definition.
(thesaurus)
'blows head off drinker' is the wordplay.
'blows head off' means to remove the first letter.
'drinker' becomes 'supper' (someone who 'sups').
'supper' with its initial letter removed is 'UPPER'.
(Other definitions for upper that I've seen before include "that's found in shoe" , "Part of a shoe; drug" , "Top of shoe; stimulant" , "Stimulant drug (informal)" , "Section of Oxford" .)