Green’s Dictionary of Slang

pox n.2

[? abbr. yen pok under yen n.1 ]

(drugs) opium.

[US] Ersine Und. and Prison Sl.
[US]Berrey & Van den Bark Amer. Thes. Sl.
[US]Anslinger & Tompkins Traffic In Narcotics 314: pox. An opium pill. Also a ration of opium prepared for smoking.
[US]J.E. Schmidt Narcotics Lingo and Lore.
[US]ONDCP Street Terms 17: Pox — Opium.