Narcotic or sedative drug (6)
I believe the answer is:
opiate
I believe this clue is a double definition.
'narcotic' is the first definition.
(I know that opiate is a type of narcotic)
'sedative drug' is the second definition.
(I've seen this in another clue)
(Other definitions for opiate that I've seen before include "A sleep-inducing drug (6)" , "A poet I become on this drug" , "Sedating drug" , "Drug with an opium base" , "dope" .)