Green’s Dictionary of Slang

1. (also geeser) an injection of a narcotic drug.

1929		E. Booth Stealing Through Life 282: I take a geezer once in a while myself.
1936		D. Maurer ‘Argot of the Und. Narcotic Addict’ Pt 1 in AS XI:2 121/2: geezer. A shot of narcotic injected hypodermically.
1937		B. Dai Opium Addiction in Chicago 199: Geeser. A shot of drugs.
1949		Monteleone Criminal Sl. (rev. edn) 96: geeser A small amount of narcotic [...] geezer An injection of a narcotic.
1953		Anslinger & Tompkins Traffic In Narcotics 308: geezer. An injection of a drug.
1959		J.E. Schmidt Narcotics Lingo and Lore.
1971		E.E. Landy Underground Dict. (1972).

2. (US) a heroin addict.

1968

N. von Hoffman We are the People Our Parents Warned Us Against 34: The Haight is a freak show, a street of poisoners, killers, geezers, burn artists.