Addictive narcotic (5)
I believe the answer is:
opium
'addictive narcotic' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for opium that I've seen before include "Derivative of Poppy" , "analgesic" , "Poppy drug" , "Narcotic derived from poppy" , "Duller" .)