Hello, I just preformed an IV of heroin (stupid, i know) and my arm and hand at first were somewhat burny/itchy, only for a few seconds, but my arm, from where I injected it on my inner elbow, bursted into a bunch of hives. Its been about 15min -20min now and the hives have gone down, but was this me hitting an artery? It didnt hurt so I dont think so. Did I cause an allergic reaction or something? Help me out Doc, Im concerned.