Sedative drug (6)
I believe the answer is:
opiate
'sedative drug' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for opiate that I've seen before include "Drug inducing a false sense of contentment" , "Drug with an opium base" , "Drug made from poppy" , "A sedative drug" , "Does it ease pain" .)