Yea bro, if you inject into a vein, you will know it pretty quick. I did it about 2 yrs ago with winny and b-12. I guess some blood came into the syringe and I didn't see it because the b-12 is red. My leg started tingling, then I broke out in kind of a rash down my leg. My lower back was itching like crazy. My butt and right leg looked like a road map. After about an hour, the pain became excruciating. I made all through the night then at 5 the next morning, I had a buddy drive me 60 miles to the closest hospital. They gave me pain pills and after about 1.5 days, it was back to normal. I have never had to use a pain pill in my life but I couldn't stand the pain with that shit. Now, I aspirate 2 or 3 times during the injection. Once at first, then again about 1/2 way through and then maybe one more time. Better to safe. Bam