Green’s Dictionary of Slang

q.p. n.

also QP

(US drugs) a quarter pound of cannabis; note def. in cit. 2002 is probably an error.

Danktuary Marijuana and Mushroom Dict. 🌐 QP [n.] One quarter ounce [sic] of pot.
[US]A. Mansbach ‘Crown Heist’ in Brooklyn Noir 126: He came by at night, picked up a QP.
Chief Keef ‘Macaroni Time’ 🎵 I gotta QP of Earth rolling, let's get high.
[US]N. Walker Cherry 248: [W]e averaged $4500/lb selling it [i.e. homegrown marijuana] off in QPs and ounces.