At are signs that someone uses drugs by injections?

Scars or marks: Usuually you can suspect someone may be using drugs via injection(iv) methods when you see multiple puncture marks on their arms (usually at the fold of the inner elbow) hands, neck, feet/toes and even woman's breasts (yep, their breasts ). Repeated abscesses (like a large pimple) can also develop at the sites where they are injecting.