Green’s Dictionary of Slang

1. (US) a beard [facial hair supposedly resembles the leaves of the tree; cognate with spinach n.² (1)].

1938

D. Runyon ‘The Big Umbrella’ in Runyon on Broadway (1954) 561: He is afraid of the guy with the sassafras.

2. (drugs) marijuana [sassafras leaves are used for tea, thus link to tea n. (4a)].

1944		Marihuana Problem in City of N.Y. in Johnson Indian Hemp (1952) 34: The cheapest brand is known as ‘sass-fras’.
1969		R.R. Lingeman Drugs from A to Z (1970) 222: sassfras marijuana cigarette.
1971		Illinois Legislative Investigating Committee Drug Crisis in Spears (1986).
1982		Abel Marihuana Dict.
2001		ONDCP Street Terms 18: Sasfras — Marijuana.