Definition of "benzedrine"

[…] who chained themselves to subways for the endless ride from Battery to holy Bronx on benzedrine until the noise of wheels and children brought them down […]

1956, Allen Ginsberg, “Howl”, in Howl and Other Poems (Pocket Poets Series), City Lights Books, page 10

Then I would be way ahead when college started at the end of September, and able to enjoy my last year instead of swotting away with no make-up and stringy hair, on a diet of coffee and benzedrine, the way most of the seniors taking honours did, until they finished their thesis.

1963, Sylvia Plath, The Bell Jar, Faber and Faber, page 118