Green’s Dictionary of Slang

cap n.4

[abbr.]

1. (drugs) a capsule containing a narcotic, usu. heroin.

[US]Spokesman-Rev. (Spokane, WA) 11 Oct. 8/4: A package of drug wrapped in paper is called a ‘deck,’ a ‘check,’ or a ‘bundle.’ If it is in a capsule it is called a ‘berry,’ a ‘bean,’ or a ‘cap’ .
[US]D. Maurer ‘Argot of the Und. Narcotic Addict’ Pt 1 in AS XI:2 119/2: cap. A bindle of heroin or morphine sold in capsules which are, incidentally, often concealed by the peddler in his rolled-up shirt cuffs, heroin in one sleeve, morphine in the other.
[US]W. Burroughs letter 30 Nov. in Harris (1993) 25: I hope to rid myself of the habit in the course of this trip. Taking along a pint of P.G. and a large supply of goof balls to taper off. Also 20 caps.
[US]‘William Lee’ Junkie (1966) 45: The H caps cost three dollars each and you need at least three a day.
[US]W. Motley Let No Man Write My Epitaph (1959) 119: An ounce makes close to five hundred [...] When I fill these caps I can make a lot.
[US]C. Cooper Jr Scene (1996) 41: Only they weren’t girls, having acquired through the years [...] of practice the names: Four Caps, Six Caps and Eight Caps.
[US]C. Brown Manchild in the Promised Land (1969) 109: I had a lot of guys stealing all kinds of caps with white powder in them.
[US]L. Wolf Voices from the Love Generation 172: Three bucks for a cap.
[US]E. Bunker No Beast So Fierce 35: The jivin‘ motherfuckers give you more time for a cap of heroin than murder.
[US]V.E. Smith Jones Men 16: I don’t have but one cap of the white bag, man.
[US]R. Sabbag Snowblind (1978) 94: He could hit you with lids, caps, keys, tabs, nickel bags, blotters, buttons, spoons and everything from milligrams to boatloads.
[US](con. 1930s) Courtwright & Des Jarlais Addicts Who Survived 192: I’ll sell them in the quarters, eights, and sixteenths, and in the small caps, and the fifty-cent packages.
[US](con. 1982–6) T. Williams Cocaine Kids (1990) 57: One day I go out they be selling for ten dollars a cap. The next day it‘s eight dollars a cap.
[US]L. Pettiway Workin’ It 157: It’s a drug war now in the projects about this one person is selling three dollar caps, and since you got three dollar caps, our five dollar caps ain’t selling.
[US]E. Bunker Mr Blue 235: ‘Just a couple caps.’ In those days heroin, at least on the streets of LA, was sold in small number 5 gelatin capsules. A cap was still potent.
[US]ONDCP Street Terms 5: Cap — [...] a capsule of a drug.

2. (drugs) a capsule of LSD.

[US]P. Wylie Esquire July 44–45: cap — a capsule of LSD.
[US] ‘Sl. of Watts’ in Current Sl. III:2.
[US]R.R. Lingeman Drugs from A to Z (1970) 59: cap [...] (2) currently, a capsule containing a hallucinogen.
[US]ONDCP Street Terms 5: Cap — [...] LSD.

3. (drugs) a capsule of any drug.

[US]H. Ellison ‘The Hippie-Slayer’ in Deadly Streets (1983) 107: Some were merely dropping dexy in pill or cap form.
[US]E. Leonard Glitz 202: He fixed two rum-and-cokes then, emptying a street-lude cap into Iris’s – eighty milligrams of Valium to take off her edge – and brought their drinks out to the living room.
[US]S. King Misery (1988) 124: He would have to cut down, have to duck some of the caps.

4. psilocybin/psilocin.

[US]ONDCP Street Terms 5: Caps — [...] psilocybin/psilocin.

5. (drugs) crack cocaine.

[US]L. Pettiway Workin’ It 111: If they do get into a little thing it’s about a cap of crack.
[US]ONDCP Street Terms 5: Cap — Crack Cocaine.

6. (US prison) a measure of marijuana: as much as can be fitted into a small cap, e.g. of a toothpaste tube or a container of chapstick.

[US]Bentley & Corbett Prison Sl. 74: A cap may also be used as a unit of measure of marijuana. A method now being used in prison is filling the inside of a toothpaste cap with marijuana and selling this amount as a ‘box bag’ or a ten dollar ‘bag’ of marijuana.
[UK]Guardian Editor 28 May 20: Cap: The marijuana that fits into a chapstick cap.
[US]Other Side of the Wall: Prisoner’s Dict. July [Internet] Cap: The amount of marijuana that fits into a chapstick cap.

In phrases

bust a cap (v.)

(drugs) to inject a shot of heroin (which comes in capsule form).

[US]C. Cooper Jr Scene (1996) 10: Why don’t you bust a cap with me?
[US]E.E. Landy Underground Dict. (1972).
cap out

(US drugs) to collapse or fall asleep after the consumption of a drug.

[US]E. Folb Urban Black Argot 134: Cap out to pass out or fall asleep from excessive marijuana or pills.