^In my two years of being on the street and living with tons of different junkies in the bay area, I never met one that had heard of or used a micron filter, sadly, especially since the heroin there is so fucked up that they could really use 'em. But yeah, I've shot dope for nearly ten years, and only used a micron filter for a period of a month or so, which was great, and I'm sure it could've prevented many cases of cotton fever/dirty shot syndrome, and probably could have saved a lot of my veins, but the point is, I'm still alive. Heroin #4 is in itself not very harmful to inject, it's what they sometimes cut it with that can cause problems, especially if you're dealing with tar, I've known dealers to cut tar dope with shoe polish.