Poppy drug (5)
I believe the answer is:
opium
'poppy drug' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for opium that I've seen before include "Poppy drug" , "Narcotic derived from poppy" , "Number" , "Dried juice of white poppy" , "Addictive drug made from poppies" .)