'Curse of marijuana' – the Mail (8)
I believe the answer is:
anathema
'curse' is the definition.
(anathema can mean a curse)
'of marijuana the mail' is the wordplay.
'of' says the answer is hidden in the clue.
'ANATHEMA' can be found hidden inside 'marijuana the mail'.
(Other definitions for anathema that I've seen before include "odious" , "Execration" , "Cursed thing" , "Formal curse leading to excommunication" , "Formal church curse of excommunication" .)