Creep and drop drug into drink (9)
I believe the answer is:
snakebite
'drink' is the definition.
(I know that Snakebite is a type of shandy)
'creep and drop drug' is the wordplay.
'creep' becomes 'snake' (snake can mean to creep or crawl along).
'and' is a charade indicator (letters next to each other).
'drop' becomes 'bit' (both can mean a small amount).
'drug' becomes 'e' (E is another name for ecstasy).
'snake'+'bit'+'e'='SNAKEBITE'
'into' acts as a link.
(Other definitions for snakebite that I've seen before include "That could be fatal!" , "strong drink" , "Cider mixed with lager" , "Mixed drink < traitor served with food" , "We may be poisoned, given this" .)