instant zen, n. — Green’s Dictionary of Slang

instant zen n.

[the contemplative world of Zen Buddhism]

(drugs) LSD.

1972		Dahlskog Dict. Contemp. and Colloq. Usage.
1977		L. Young et al. Recreational Drugs.
1982		AS LVII:4 289: A sampling of current names for varieties of LSD would include [...] instant Zen.
2001		ONDCP Street Terms 12: Instant zen — LSD.