The Collaborative International Dictionary of English v.0.48:

bennie \ben"nie\ n.
   a slang name for Benzedrine, a trademark for one brand of
   amphetamine; -- also used generically for any brand of
   amphetamine. [slang] [Also spelled benny.]

   Syn: Benzedrine.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

bennie
    n 1: a form of amphetamine [syn: Benzedrine, bennie]