Green’s Dictionary of Slang

1. (also off at the head) insane, out of one’s mind.

1842		T. Hood ‘Turtles’ Works (1862) VI 5: And now along that fatal Hill they pass / Where centuries ago an Oxford bled, / And proved – too late to save his life, alas! – / That he was ‘off his head’.
1879		G.R. Sims Dagonet Ballads 122: I can’t contain myself, I’m off my head with joy.
1883		E.J. Milliken Childe Chappie’s Pilgrimage 20: A cropper I’ve come, but it shall not be said / That this Johnny’s a cocktail blue-funked off his head.
1888		‘Rolf Boldrewood’ Robbery Under Arms (1922) 99: He’s gone off his head and stopped in some swell town in New Zealand — Canterbury, I think it’s called.
1890		Music Hall & Theatre Rev. 26 July 11/1: [He] inclines to the opinion that he must have been rather off his head for the last few months.
1894		H. Lawson ‘A Respectable Young Man’ in Roderick (1972) 270: The poor fellow was nearly off his head with trouble.
1903		J. Furphy Such is Life 287: That chap’s no more off his head than I am. Bit odd, I daresay; but that’s nothing.
1910		Magnet 27 Aug. 1: Are you off your silly onion?
1913		Sport (Adelaide) 15 Feb. 11/3: They Say [...] That T M has gone off his head with the Roxy.
1914		Bulletin (Sydney) 24 Sept. 11/1: If yer wasn’t off yer onion, Kaiser Bill, / Would yer tread on Russia’s bunion, Kaiser Bill? / Would yer spring up mad an’ perty, / Let yer right go loose an’ dirty, / Till yer neighbors all got shirty, Kaiser Bill?
1922		‘Sapper’ Black Gang 412: They’d think I was off my head.
1922		Wodehouse Clicking of Cuthbert 5: You’re right off it.
1930		H. Ashton Doctor Serocold (1936) 172: She was quite off her head about him for a month or two.
1945		F.J. Hardy Man From Clinkapella 4: I’d rather get blown to pieces than go off my head.
1957		A. Buckeridge Thanks to Jennings (1988) 177: Were the boys off their heads, he wondered!
1959		W.M. Branham ‘Abraham’s Seed’ Sermon, delivered on 23 Apr. at the Santa Clara County Fairgds in San Jose, USA, on nathan.co.za 🌐 ‘Yes, sir. I--I... What is your address? I--I’ll call you later.’ Whew, he’s off at the head.
1970		T. Parker Frying-Pan 136: I must be off my fucking head coming to do it.
1981		(con. 1920s) P. Crosbie Your Dinner’s Poured Out! 158: Once I went to Colney Hatch, / Saw a lovely batch, / Of people off their thatch.
1987		B. Chatwin Songlines 131: The Governor was off his head.
1998		P. McCabe Breakfast on Pluto 54: He’s off his fucking head!
2000		Indep. Rev. 20 Jan. 7: You’re off your head! Your mind’s totally screwed!
2002		Sydney Morn. Herald 18 Jan. 59/3: I was so offit, I just stood there facing this guy, who [...] was pointing a big f—ing gun at me.
2010		L. Redhead Thrill City [ebook] I don’t know what you’re talking about. You’re off your head.

2. drunk.

1883		Bristol Magpie 3 Mat 4/1: The Chairman: You will have to prove what you say, Mr. Curtis. You seem to be off your head altogether. Mr. Curtis: You offered to fight anybody.
1901		Truth (Brisbane) 12 May 7/3: Now the slavey's taken akshun / For the things the missus sed, / Right in front of him in Karkee, / The day as she was off her hed.
1999		Guardian Editor 25 June 12: Let’s get off our heads till we drop.

3. (drugs) intoxicated by a drug.

1985		R.G. Barrett You Wouldn’t Be Dead for Quids (1989) 147: Here she was [...] tripping off her head.
1999		Guardian Guide 22–28 May 24: The mind-expanding substance [...] which gets you equally effectively off your bonce.
2004		L. Redhead Peepshow [ebook] Man, he was off his head. It [i.e. MDMA] was hitting him in waves, each one more powerful.