Psychotherapy has been shown to be very helpful in assisting the person learn other ways of dealing 
with their emotional pain and teaching self-soothing and distress tolerance leading to an increased self-esteem.
The most important factor is for there to be a good relationship between the client and the therapist. There are many different types of therapy, Gestalt therapy, Mindfulness therapy, Dialectical Behavioural therapy, Cognitive therapy object relations therapy to name a few. It is important that the therapist provide a safe “holding environment” where the client begins to learn to tolerate distress and to practice not cutting, or to restrict cutting to a very small area. At the same time the client learns to self soothe. Being realistic therapy may take up to 100 sessions but some clients require a much shorter length of therapy.
Does medication help? Certainly the SSRI antidepressants help by increasing the brain’s calming neuro chemical serotonin. Also the major tranquillisers /mood stabilizers e.g. Quetiapine do help some people.