Green’s Dictionary of Slang

(US drugs) marijuana.

[1906		A. Adams ‘At Commanche Ford’ Cattle Brands 🌐 The horses had strayed [...] and when we found them they were cutting up as if they had been eating loco weed for a month].
1917		Butte Dly Post (MT) 2 Nov. 7/7: Loco weed by the bucketful was seized yesterday by the police [...] The officers found a washtub [...] filled with marijuana weed.
1924		Wash. Post 6 Jan. n.p.: ‘Marihuana,’ or ‘Marijuana’ as some spell it, the everyday ‘loco weed’ that formerly grew wild on the deserts of northern Mexico, now is being cultivated for sale to addicts of the plant in this country.
1927		S.V. Benét John Brown’s Body (1928) 40: When the news of Beckhams death spread from bar to bar, It was like putting loco-weed into whiskey.
1931		Irwin Amer. Tramp and Und. Sl. 122: The ‘loco weed’ is a variety of the marajuana [sic] which is much used as a drug by Mexican Indians. Not unlike Indian hemp, cannabis sativa, its use produces a mild exhilaration and elaborate dreams, but does not appear to set up a habit as does the use of other drugs.
1946		Ella Fitzgerald & The Ink Spots ‘Cow Cow Boogie’ 🎵 He was raised on locoweed / He’s what you call a Swing halfbreed.
1955		Kerouac letter 12 Oct. in Charters I (1995) 523: Even old farmers have it growing in their backyards and call it loco weed.
1966		H.S. Thompson Hell’s Angels (1967) 221: If Horatio Alger had been born near a field of locoweed his story might have been a lot different.
1976		R. Sabbag Snowblind (1978) 80: Colombian-locoweed marijuana had just hit the headlines [...] Colombian dope, overnight, had become a growth industry.
1989		H. Rawson Dict. of Invective (1991) 239: Marijuana also is known in some circles as locoweed.
1998		A. Warner Sopranos 57: The three of them getting spluttering on stupid loco weed.
2000		T. Udo Vatican Bloodbath 82: You fucken been fucken smoking that godamn fucken loco fucken weed!