Green’s Dictionary of Slang

(US drugs) a regular smoker of marijuana.

1950		Goldin et al. DAUL 200/1: Snake. 1. An habitual smoker of marijuana.
1956		(con. 1940s) J. Resko Reprieve 237: An addict is a viper, a snake, a goof, a T-man. In Dannemora we had mostly vipers, with the exception of a small, exclusive, super-hep group in which ‘snake’ was the label of distinction.