As it happens, rear part of bar is what gets damaged after too much drink is taken (5)
I believe the answer is:
liver
'bar is what gets damaged after too much drink is taken' is the definition.
I can't tell whether this defines the answer.
'as it happens rear part' is the wordplay.
'as it happens' becomes 'live' (as in live television).
'part' suggests taking the first letters.
The initial letter of 'rear' is 'r'.
'live'+'r'='LIVER'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for liver that I've seen before include "Part of body" , "Viler (anag.)" , "Internal organ" , "Dark reddish brown" , "Glandular organ of the stomach" .)