Green’s Dictionary of Slang

1. (drugs) under the influence of LSD or another hallucinogen.

1970		Arizona Dly Star (Tucson, AZ) 19 Jan. 5/2: Brody [...] made his decision to give away what he calls a $25 million inheritance while ‘I was tripped out on drugs’.
1986		Anniston Star (AL) 10 Apr. 23/2: .
1999		Guardian Guide 14–20 Aug. 12: Old guys doing switched-on, tripped-out tribal music.
2002		Hattiesburg American (MS) 28 Feb. 43/1: The Tripped Out Hippie Chicks [...] stole the show.

2. disorientated, confused, upset.

1971		E.E. Landy Underground Dict. (1972).
1992		R.C. Cruz Straight Outta Compton 9: House niggers who weren’t even invited to sit on the stoop gave Flip, Billy’s tripped-out friend, an excuse to follow suit.
2000		J.J. Connolly Layer Cake 174: I reckon I’d better eat cos otherwise I’m gonna get more light-headed, more and more tripped out.