Poison's drunk in scare (7)
I believe the answer is:
arsenic
'poison's' is the definition.
(thesaurus)
'drunk in scare' is the wordplay.
'drunk' indicates anagramming the letters.
'in'+'scare'='inscare'
'inscare' anagrammed gives 'ARSENIC'.
(Other definitions for arsenic that I've seen before include "Element No 33" , "Powerful poison" , "Poisons in scare" , ", it goes with old lace" , "killer" .)