Green’s Dictionary of Slang

1. one who ‘plays around’ with drugs, esp. amphetamines or barbiturates.

1952		(con. 1948) G. Mandel Flee the Angry Strangers 434: The talkers and the goofers were packed around coffee-drenched tables.
1967		J.B. Williams Narc. and Halluc. 112: Goofer — One who drops pills.
1971		E.E. Landy Underground Dict. (1972).

2. often in pl., a barbiturate.

1954		M. Rubin ‘Gold Ring’ in Margulies Back Alley Jungle (1963) 97: Harold came a half-hour later, carrying the goofers in a briefcase.
1966		F. Elli Riot (1967) 23: ‘Doc,’ one called, ‘got any goof-balls on ya?’ [...] ‘Yeah,’ the other said, ‘give us some goofers.’.
1977		L. Young et al. Recreational Drugs.
2001		ONDCP Street Terms 10: Goofers — Depressants.