A sound out around intravenous drugs?

when junkies talk about needing to find a foreign vein because the one they've been shooting into has be worn out, what do they mean? that the whole vein have literally been damaged by the drugs, or that they have so plentiful puncture holes there's no room, or that the vein has lost its receptivity and they can't grasp as good a high from that vein any more....? these are my speculations. i enjoy no idea what the truth is though.
Answers:
Building off of the above answer, once the veins sclerose or harden/scar over, the radius of the blood vessel decrease and the blood therefore doesn't flow as well through the vessel.
There are a lot of things that develop, but mostly they sclerose. Basically, that's just a matter of scarring down, and it may not be the drugs themselves but all the crud within there with the drugs, or that they aren't exactly in isotonic solution. Your average heroin user isn't an especially meticulous chemist.

Related Questions:
Why do I own such a glorious resistance to any medication?   I smoked pot a while wager on, will i ratify a drug check?   Methadone,xanax, and unsullied added from pdoc lamictail?   How long does Prozac stay surrounded by your blood?   Could my coital headache be related to my retarded ejaculation?  
  • What technology do pharmacists use?
  • Please Help me!! Medical problem?
  • Are at hand any Bible versus that show the use of medication, or someone seeing a doctor?