Green’s Dictionary of Slang

hazel n.1

[its colour; note witch-hazel n.]

(drugs) heroin.

[US]Monteleone Criminal Sl. (rev. edn).
[US]Anslinger & Tompkins Traffic In Narcotics 310: hazel. Heroin.
[US]ONDCP Street Terms 11: Hazel — Heroin.