This is a disorder not fully understood. Like anorexia and bulimia if not caught early could cause permanent physical damage. The most unusual fact about why cutting becomes so addicting is because of the release of endorphns which temporarily make the emotional pain go away. This behavior at the very least leaves scars, physical and emotional on an already traumatized child (or do you believe that it's just another way for kids to get high?? Please don't think that. When the pain switches from emotional to physical it energizes the body to prepare to ward off danger.
Treatment must be based on the causes of bulimia. If after evaluation and stabilization, humanistic psychotherapy, family therapy, EMDR for the traumas that lead to cutting, medications, and the involvement of your internist. The treatment for anorexia, bulimia, and cutting are all team approaches. These three conditions are very serious and if you are a parent who thinks this is just a stage, a way to fit in, or a way to get high, get help for yourself. You are in serious denial. Your child could suffer permanent damage.