Spike the demon drink (6)
I believe the answer is:
impale
'spike' is the definition.
('impale' can be a synonym of 'spike')
'the demon drink' is the wordplay.
'the demon' becomes 'imp' (I've seen this before).
'drink' becomes 'ale' (ale is a kind of drink).
'imp'+'ale'='IMPALE'
(Other definitions for impale that I've seen before include "go through with it" , "Skewer" , "Kill by piercing with a sharp stake" , "Pierce, me pail (anag.)" , "spit!" .)