dog food, n.⁴ — Green’s Dictionary of Slang

dog food n.⁴

[ext. of SE use; ? its colour (brown) or the low status of its users]

(drugs) heroin.

1980		E. Folb Runnin’ Down Some Lines 172: Several terms were used to characterize heroin – [...] smack, shit, dog food.
1985		T.R. Houser Central Sl.
1992		Bentley & Corbett Prison Sl. 49: Dog Food A black expression used to mean heroin.
2001		ONDCP Street Terms 8: Dog food — Heroin.
2016		(ref. to mid-1970s) M. Carey ‘Bad News’ 101: ‘Marvin was experimenting with heroin [...] Back in those days we called the stuff “dog food”’.