Lager and cider: you'll need an antidote for it! (9)
I believe the answer is:
snakebite
This clue is a double definition.
'lager and cider' is the first definition.
(alcoholic drink made of cider and lager)
'you'll need an antidote for it' is the second definition.
(Other definitions for snakebite that I've seen before include "Cider and lager - it could be poisonous" , "Drink made of lager and cider" , "Cider mixed with lager" , "Drink (dangerous if given by 18!)" , "Mixture of drinks" .)