Scruff takes ecstasy, seeing little sleep ahead (4)
I believe the answer is:
nape
'scruff' is the definition.
('nape' can be a synonym of 'scruff')
'ecstasy seeing little sleep ahead' is the wordplay.
'ecstasy' becomes 'e' (informal term for the drug).
'seeing little sleep' becomes 'nap' (I've seen this before).
'ahead' means one lot of letters go next to another.
'e' after 'nap' is 'NAPE'.
'takes' acts as a link.
(Other definitions for nape that I've seen before include "Back part of the neck" , "Scruff of the neck" , "sofa" , "Here's a hairline" , "It's a pane in the neck" .)