Those legally in possession of drugs needing no introduction (6)
I believe the answer is:
owners
'those legally in possession' is the definition.
I can't tell whether this defines the answer.
'drugs needing no introduction' is the wordplay.
'drugs' becomes 'downers' (downer is a kind of drug).
'needing no introduction' means to remove the first letter.
'downers' with its initial letter taken off is 'OWNERS'.
'of' is the link.
Can you help me to learn more?
(Other definitions for owners that I've seen before include "Legal possessors" , "Holders, possessors" , "Proprietors" , "Those in lawful possession, as of house" , "Worsen for possessors" .)