Hi, Thanks for writing to us, Few of the common complications of self injecting intravenously is hematoma, where blood leaks out of the vein during removal of the needle due to inadequate pressure applied. There can be infiltration or leakage of the substance in the syringe into adjacent tissues apart from inside the vein which can be toxic to those tissues. There can be inflammation of the vein leading to phlebitis which may also be an infection if adequate sterility is not maintained during the injection. If your arm is tense, painful and bruised, it needs to be examined by a medical professional to determine the cause and the extent of damage caused. The treatment would be appropriately given according to the findings. Hope your query is answered. Dr Anjana Rao Kavoor