Green’s Dictionary of Slang

(drugs) dimethyltriptamine.

1969		R.R. Lingeman Drugs from A to Z (1970) 31: AMT [...] amphetamines.
1971		in R.G. Reisner Graffiti 129: Tea is a groove and AMT is really boss.
2001		ONDCP Street Terms 1: AMT — Dimethyltryptamine.
2009		‘What Police Must Learn’ in Dly Teleg. 8 Nov. 🌐 amt — dimethyltriptamine.