Green’s Dictionary of Slang

1. (orig. US) an eccentric, a mad person; one who has a split personality.

1955		W. Gaddis Recognitions I. v. 196: I’ve heard about her [...] On the needle. A schiz.
1972		N.Y. Times Book Rev. 16 July 30: 300-pound Leland, an intermittently brilliant schiz, is going berserk in the basement.
2000		Guardian Guide 5–11 Feb. 8: Sorry-ass niggaz; pussy niggaz; white niggaz; skizzaz; dumb muthafuckas.
2001		J. Stahl Plainclothes Naked (2002) 261: Is it me, Mac, or are you some kind of a schiz? Half the time you sounds straight outta Compton, the other half I’m thinking, ‘This guy majored in humanities at Dartmouth.’.

2. (US black/drugs) stimulation from crack cocaine.

1996

L. Pettiway Honey, Honey, Miss Thang 66: [in a crack house] I guess my schitz is watching others schitz [...] I get a kick from watching them feel around and look for things when I know there’s nothing there. [...] I get simple when I smoke crack.