garbage, adj. — Green’s Dictionary of Slang

garbage adj.

1. mediocre, socially inferior.

1963		in T.I. Rubin Sweet Daddy 66: [The] kids came from the garbage side of the tracks.
2005		W.D. Myers Autobiog. of My Dead Brother 159: Dad said it used to be only the white papers that ran all the garbage news about black people.

2. (drugs) of drugs, potentially dangerous, likely to cause harmful side effects.

1979		H. Feldman et al. Angel Dust 128: It’s [i.e phencyclidine] a garbage drug anyhow.
1981		D.E. Miller Bk of Jargon 341: garbage drugs: Glue sniffing, PCP, and other drugs that have a high likelihood of adverse effects.

In compounds

garbagehead (n.)

(US) in the context of drug use, a gullible fool.

1994

R. Moody Ice Storm 84: Paul was a garbage head! A loser, as they were called among stoners. Paul bought oregano and thought it was good shit. [...] He had smoked a Quaalude; he had overdosed on cold pills.