My Friend Shot Up Meth And His Four Arm Above

My friend shot up meth and his four arm above his elbow or blow it over whatever and it is growing into it was a wide red patch on his arm was hurting bad still is hurting but it's gone into more of a head because we've been hitting it and I want to know is that the right thing to do but should be done it's hot in the area where the pump is then his whole hurts