Green’s Dictionary of Slang

(US prison) heroin.

1997		T. Fontana ‘Straight Life’ Oz ser. 1 ep. 5 [TV script] Tits. That’s what we in prison call drugs.
2000		Other Side of the Wall: Prisoner’s Dict. July 🌐 Tit: Drugs, heroin.
2000		T. Fontana ‘Bill of Wrongs’ Oz ser. 4 ep. 3 [TV script] Hernandez, Adebisi and me have been partners selling tits.
2001		ONDCP Street Terms 21: Tits — Black tar heroin.