Green’s Dictionary of Slang

straight shooter n.2

1. one who injects narcotics.

[US]Current Sl. III–IV (Cumulative Issue).

2. (also straight) a hypodermic, a syringe.

[US]L. Pettiway Workin’ It 178: Go get my straight shooter. [Ibid.] 181: You got a straight on you?

In phrases

straight line shooter (n.)

(US drugs) a drug addict who injects into the vein.

[US]‘Goat’ Laven Rough Stuff 118: Others shoot right into the artery, these straight line shooters tie something round their arm just above the elbow joint.