Old illicit traders disposing of the last of their drugs (7)
I believe the answer is:
opiates
'drugs' is the definition.
(opiate is a kind of drug)
I don't understand how the remainder of the clue works.
(Other definitions for opiates that I've seen before include "Is a poet (anag.)" , "Sedative drugs" , "Narcotic drugs" , "Poppy-derived drugs" , "Branch of narcotics" .)