Possesses marijuana but not heroin (3)
I believe the answer is:
has
'possesses' is the definition.
('have' can be a synonym of 'possess')
'marijuana but not heroin' is the wordplay.
I cannot quite understand how this works, but
'heroin' could be 'h' (H is a slang term for heroin) and 'h' is found in the answer.
The remaining letters 'as' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for has that I've seen before include "suffers from" , "Gives birth to" , "Cheats" , "Possesses or owns" , "Eats" .)