hot and cold, n.¹ — Green’s Dictionary of Slang

hot and cold n.¹

[initial letters, plus fig. ref. to the effects of the drugs]

(US drugs) a combination of heroin and cocaine.

1971		E.E. Landy Underground Dict. (1972) 196: hot and cold n. (d) Heroin and cocaine. Comes from the fact that heroin and cocaine are opposites; heroin depresses the body and cocaine tends to stimulate it. a.k.a. H and C.
1975		personal record in Spears Sl. and Jargon of Drugs and Drink (1986).