Late drink that may go to the head (8)
I believe the answer is:
nightcap
'late drink that may go to the head' is the definition.
'nightcap' can be an answer for 'late drink' (drink drunk late at night). I am not certain of the rest of the definition.
'late drink' is the wordplay.
'late' becomes 'night' (I've seen this before).
'drink' becomes 'cap' (I can't justify this - if you can you should believe this answer much more).
'night'+'cap'='NIGHTCAP'
Can you help me to learn more?
(Other definitions for nightcap that I've seen before include "Old headgear" , "Last drink of the day?" , "that may go to one's head?" , "drink having sleepy effect?" , "A drink before sleep" .)