Most self-cutters are very depressed people. This kind of depression is of a physical kind that usually does not respond to 'talk therapy'.
If you want to have them treated without recourse to drugs you will need to see a therapist, trained in nutritional psychology.
Most self-cutters are found to be hypoglycemic, that is a disease of energy production. Without that energy the brain cannot produce the feel good neurotransmitters such as serotonin. Most doctors tend to prescribe ssris, but these are not likely to treat the underlying causes of serotonin deficiency. This is more like a nutritional disorder, involving insulin resistance.
Please discuss with a nutritional doctor.
Jurriaan plesman