Green’s Dictionary of Slang

george (smack) n.

[George adj. (2) + smack n.2 (1)]

(US drugs) high-quality heroin.

[US]Maurer & Vogel Narcotics and Narcotic Addiction (3rd edn).
[US]Hardy & Cull Drug Lang. and Lore.
[US]ONDCP Street Terms 10: George — Heroin.