Green’s Dictionary of Slang

(drugs) Benzedrine; thus B-head, a user of Benzedrine.

1952		Lannoy & Masterson ‘Teenage Hophead Jargon’ AS XXVII:1 24: B, n. Benzedrine.
1961		H. Ellison Rockabilly (1963) 61: He’ll probably want a few of those little Bufferin B’s zonking around in his system.
1963		J. Rechy City of Night 174: We’ll get tanked on bees and pod.