Article on drink: a cause of pain (6)
I believe the answer is:
angina
'cause of pain' is the definition.
(angina is a type of chest pain)
'article on drink a' is the wordplay.
'article' becomes 'an' (English indefinite article).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'drink' becomes 'gin' (gin is an alcoholic drink).
'an'+'gin'+'a'='ANGINA'
(Other definitions for angina that I've seen before include "Sudden cardiac pain" , "Heart ailment" , "Painful heart complaint." , "Cardiac complaint" , "chest complaint" .)