Green’s Dictionary of Slang

1. (US drugs) to mix together cocaine and heroin.

1983

N. Heard House of Slammers 58: We up and decide to, like, dip a little bit together.

2. (N.Z. drugs/prison) to take LSD.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 56/2: dip v. (also go dipping) to take LSD.