Halfwit (4)
(Other definitions for dope that I've seen before include "Illegal drugs; fool" , "Booby" , "Illegal drug; idiot" , "Fool - cannabis" , "Sucker" .)
'halfwit' is the definition.
(halfwit can mean a foolish person)
This is all the clue.
(Other definitions for fool that I've seen before include "Deceive" , "Jester or silly ass" , "Dupe - dessert" , "Idiot" , "Empty-headed person" .)