Unconscious mental pressure to have a drink before attempt (8)
I believe the answer is:
superego
'unconscious' is the definition.
(thesaurus)
'a drink before attempt' is the wordplay.
'a drink' becomes 'sup' (to sup is to drink).
'before' becomes 'ere' (poetic term for 'before').
'attempt' becomes 'go' (go is a kind of attempt).
'sup'+'ere'+'go'='SUPEREGO'
'mental pressure to have' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for superego that I've seen before include "Internal monitor of psyche" , "Freudian concept of conscience" , "Moral part of the (Freudian) unconscious" , "See group (anag.)" , "Part of mind acting as conscience" .)