Green’s Dictionary of Slang

(drugs) phencyclidine.

1973		C. Gaines Stay Hungry 146: I’ve done it all, man, glue, mushrooms, twenty-five, turps, Nembutal, THC, hash ... I been weird every way there is.
1979		H. Feldman et al. Angel Dust 74: Phencyclidine is available today under a wide array of street names: T, P, tish or titch, peep, THC [...] the most common names, however, are PCP or P, buzz, THC or T.