Green’s Dictionary of Slang

1. (drugs) one who takes LSD or similar hallucinogens.

1969		L. Yablonsky Hippie Trip 268: A large mental hospital population of psychotic ‘bum-trippers.’.
1971		E.E. Landy Underground Dict. (1972).
1977		H. Garner Monkey Grip 215: I put my hand on his arm (tripper’s privilege).
2004		L. Redhead Peepshow [ebook] The tripper staggered out of the Palace nightclub into the bright hideousness of dawn.

2. in fig. use, one who leads a surreal life.

1987

(con. 1967) E. Spencer Welcome to Vietnam (1989) 96: Pilots [...] go from a fire fight and a hot L.Z. to cold beer in an air-conditioned bar in half an hour or so. Tell me you wouldn’t be a tripper if you did that shit for a while.