Green’s Dictionary of Slang

prodder n.

[prod v. (2)]

(drugs) one who injects narcotics.

[UK]E. Murphy Black Candle 241: The addict, or ‘prodder’ usually melts the tablet in a teaspoonful of water over gas.
[US]A.J. Pollock Und. Speaks n.p.: Prodder, an addict who uses a hypodermic outfit.