Green’s Dictionary of Slang

an experience created by a hallucinogenic drug.

1969		R.R. Lingeman Drugs from A to Z (1970) 52: bum bend [...] A psychotic or panic reaction to lsd-25 or stp.
1970		K. Mackey Cure 15: Semi-hallucinogen, painkiller, and hypnotic. A pretty good oral bend, and efficient knockout brew to boot.