Green’s Dictionary of Slang

(US drugs) a narcotics addict.

1929		C.G. Givens ‘The Chatter of Guns’ in Sat. Eve. Post 13 Apr.; list extracted in AS VI:2 (1930) 131: bangster, n. Dope fiend.
1950		Goldin et al. DAUL 23/1: Bangster. A drug addict who takes injections by hypodermic needle.
1953		Anslinger & Tompkins Traffic In Narcotics 303: An addict who takes drugs by injection, a bangster.
1959		J.E. Schmidt Narcotics Lingo and Lore.
1960		(con. 1950-1960) R.A. Freeman Dict. Inmate Sl. (Walla Walla, WA) 5: Bangster – one who uses narcotics; a hype; hygelo, etc.