Sedative lawyers munched on, back from rave (9)
I believe the answer is:
barbitone
'sedative' is the definition.
(I know that barbitone is a type of barbiturate)
'lawyers munched on back from rave' is the wordplay.
'lawyers' becomes 'bar' (the bar can mean the legal profession).
'munched' becomes 'bit' (munch can mean to bite).
'back from' indicates one should take the final letters (the letter at the back of the word).
The final letter of 'rave' is 'e'.
'bar'+'bit'+'on'+'e'='BARBITONE'
(Other definitions for barbitone that I've seen before include "Drug" , "Sleeping aid" , "sedative" .)