A human staggered, inhaling foul air, the dope! (9)
I believe the answer is:
marihuana
'the dope' is the definition.
('marihuana' can be a synonym of 'dope')
'a human staggered inhaling foul air' is the wordplay.
'staggered' indicates anagramming the letters.
'inhaling' means one lot of letters goes inside another.
'foul' indicates anagramming the letters.
'a'+'human'='ahuman'
'ahuman' with letters rearranged gives 'mhuana'.
'air' is an anagram of 'ari'.
'mhuana' going around 'ari' is 'MARIHUANA'.
(Another definition for marihuana that I've seen is " Illegal drug (alt. spelling)".)