Green’s Dictionary of Slang

(drugs) dimethyltryptamine.

1966		H.S. Thompson Hell’s Angels (1967) 223: A few will [...] on top of everything else shoot some methydrine or DMT and turn into total zombies for hours.
1971		J. Mandelkau Buttons 16: Ken Kesey and the Merry Pranksters turn on the Angels to LSD, DMT, and Christ knows what.
1997		J. Birmingham Tasmanian Babes Fiasco (1998) 227: A considerable stash of marijuana, acid and DMT.
2001		ONDCP Street Terms 8: DMT — Dimethyltryptamine.