Green’s Dictionary of Slang

(US black) a mixture of cocaine and heroin.

1969		R.R. Lingeman Drugs from A to Z (1970).
1979		‘Iceberg Slim’ Airtight Willie and Me 78: I hung up and cooked a ‘C’ and ‘H’ speedball stew for breakfast.
1980		E. Folb Runnin’ Down Some Lines 172: One additional expression – a wry euphemism – was used to refer to either cocaine or heroin: C and H pure cane sugar from Hawaii.