Green’s Dictionary of Slang

brown stuff n.

[stuff n. (5); the colour]

1. as the colour of drink or drugs.

(a) (Aus./US) whisky.

[Aus]Bulletin (Sydney) 3 Dec. 36/1: And the welcome of the others, shall it ever be forgot? / ‘Is it beer, old chap, or brown-stuff, or a spiced ale steaming hot?’ / But the pilgrim, home returning, does the needful for the lot / Down in old Bohemia.
[US]T. Robinson Rough Trade [ebook] ‘Oh yeah. You’re clean now [...] Not even a drop of the brown stuff [i.e. bourbon]’.

(b) (US drugs) opium.

L. Wilson Broken Journey 20: His left hand was molding a ball of brown stuff in the hot bowl as he inhaled the fumes with a taut anxiety.
[US]‘William Lee’ Junkie (1966) 155: Brown Stuff, or Mud . . . Opium.
[US]R.R. Lingeman Drugs from A to Z (1970).
[US]Quintessence Int’l 6 4-6 69: Raw opium (‘brown stuff’). Raw opium contains protein, resin and about 20% alkaloid, the opiate.

(c) (US drugs) Mexican heroin.

[US]E.E. Landy Underground Dict. (1972).
[US]E. Little Another Day in Paradise 148: Now we got a connection for this brown stuff.

2. (also brown baby) excrement, also used fig., i.e. ‘the shit’.

[UK]K. Amis letter 8 Jan. in Leader (2000) 253: I’ll never be Joyce or Warwick Deeping, so where do I stand? In the brown stuff, it seems.
[US]T.I. Rubin In the Life 1: Crap! You know, the brown stuff. Shit, man.
[US]T.R. Houser Central Sl. 12: brown baby A bowel movement.
[UK]F. Taylor Auf Wiedersehen Pet Two 171: I think the boys from the brown stuff just arrived!
[UK]Guardian Rev. 25 June 5: Her useless chump of a husband lands them both in the brown stuff.
[UK]J.J. Connolly Layer Cake 139: You know I’d never print anything that would drop you in the proverbial brown stuff.
[Scot]T. Black Gutted 121: I was seriously up to my neck in the brown stuff.