Warning of endless damage facing heavy drinker? (9)
I believe the answer is:
harbinger
'warning' is the definition.
(I've seen this before)
'endless damage facing heavy drinker?' is the wordplay.
'endless' means to remove the last letter.
'damage' becomes 'harm' (synonyms).
'facing' means one lot of letters go next to another.
'heavy drinker?' becomes 'binger' (someone who binges).
'harm' with its last letter taken away is 'har'.
'har'+'binger'='HARBINGER'
'of' acts as a link.
(Other definitions for harbinger that I've seen before include "One giving advance warning" , "One announcing approach" , "Early sign" , "Precursor" , "sign of things to come" .)