jam, n.⁵ — Green’s Dictionary of Slang

jam n.⁵

1. (US black/drugs) cocaine.

1972		Milner & Milner Black Players 23: Sometimes one would be selling or merely ‘holding’ jam (cocaine) or weed.
1989		J. Morton Lowspeak.
2001		ONDCP Street Terms 12: Jam — Cocaine.

2. (US drugs, also jammie) amphetamine.

1998		L. Stringer Grand Central Winter (1999) 144: Sometimes they come out with three-dollar jammies.
2001		ONDCP Street Terms 12: Jam — [...] amphetamine.

jam cecil (n.) [? cecil n.²]

(drugs) amphetamine.

1975		Hardy & Cull Drug Lang. and Lore.
2001		ONDCP Street Terms 12: Jam cecil — Amphetamine.

jam house (n.)

(US black) a place where cocaine can be both purchased and then snorted in convivial surroundings.

1972

Milner & Milner Black Players 24: Jam houses where mainly men ‘snort’ cocaine and smoke marijuana.