I can't say as I have the foggiest.
I don't really know any junkies either so I can't ask or observe.
My tat wasn't done for that purpose though, not that its really in an area one could inject into (shoulder blade area, a black panther/melanistic leopard in a rearing pose, growling and with one paw going to strike, with claws unsheathed)
Where practical though, best practice is to rotate entry sites to give veins time to keep healed, and to use the finest gauge point obtainable/useable with the substance being used. I myself favour a 30 or 31ga needle for most things, other than the MS contins, those are a fucking right bugger to filter and draw up, in the case of those lil fuckers a 28ga is much more effective in prepping it.
The smaller the better basically, although the tiny ones are somewhat harder to use, less pain, far less tendency to leave track marks, but slow to deliver the payload in the rig when the plunger is pushed, due to of course, there being less space for it to flow down. They also twist, and are harder to register (after inserting the needle, you pull back slightly on the plunger, to draw blood back into the barrel, if its in the vein, then this will happen, if you are off target, then it will not do so. And with the narrower needle its easier than with a wider point for it to slip out and 'un-register', due to less resistance.)
30 and 31-32ga. spikes need a bit of finesse to use with success really.
