Ply with beer, knocked back with tablet? (6)
I believe the answer is:
regale
'ply' is the definition.
(regaling is a kind of plying)
'beer knocked back with tablet?' is the wordplay.
'beer' becomes 'lager' (lager is a kind of beer).
'knocked back' says the letters should be written in reverse.
'with' is a charade indicator (letters next to each other).
'tablet?' becomes 'e' (E can mean ecstasy or an ecstasy tablet).
'lager' back-to-front is 'regal'.
'regal'+'e'='REGALE'
'with' acts as a link.
(Other definitions for regale that I've seen before include "Supply copiously" , "Entertain, delight" , "Fete" , "Amuse with stories" , "Shower" .)