What causes discoloured painful hard lump after taking a heroin shot?

Brief answer...not to worry at the moment Detailed answer.... Hello, Thanks for the query. It looks like due to small extravasation of blood in surrounding tissues due to improper injection. There is nothing to worry at the moment. You can apply some ice locally which should settle the pain and swelling would get reduced overtime as the extravasated blood gets reabsorbed by the system. The problem occurs if swelling doesn't resolve and becomes red,painful and locally hot.Such an event would mean development of pus locally. In such a scenario,you would need to consult a doctor for drainage and prescription of antibiotics. I hope it helps,however you may revert to me for any further query. Best of luck Thanks