<s>[INST] I have a friend who shoots up opiates on occasion. He did it yesterday and today he has a very hard and painful bulge on his arm near the injection site but not at the injection site. He didn t miss the vein. So he is wondering what this bulging knot could be? And what he can do to make it go away? [/INST] Hello, I have studied his case and I think that he may have developed thrombophlebitis of the veins. This is causing pain and feeling of knot. I would recommend you to apply hot water fomentation. Also, oral antibiotics are needed. Thrombocyte ointment should be applied. I hope this knot will resolve soon. If it increases in size than he needs to show it to surgeon. I hope this answer will be useful for you. Let me know if there is any other followup questions. Thanks </s>