catnip, n. — Green’s Dictionary of Slang

catnip n.

[the US name for UK catmint; gullible buyers might well be sold bags of catnip (Nepeta cataria) or 50% catnip and 50% marijuana; Burroughs, The Naked Lunch (1959): ‘Catnip smells like marijuana when it burns. Frequently passed on the incautious or uninstructed’]

(drugs) inferior or fake marijuana.

1969		R.R. Lingeman Drugs from A to Z (1970) 59: catnip The strong-smelling herb, Nepeta cataria, sometimes sold as marijuana to an unsuspecting buyer and sometimes actually smoked for alleged hallucinogenic effects.
1971		E.E. Landy Underground Dict. (1972).
1980		E. Folb Runnin’ Down Some Lines 170: This cat come to me, gonna sell me some catnip – it smell like weed, it look like weed, but it ain’t weed.
2001		ONDCP Street Terms 5: Catnip — Marijuana cigarette.