What is the best treatment for teens who self-harm by cutting?

No simple answer. There should be a good psychiatric evaluation, then an appropriate treatment plan be developed.
DBT. Dialectical Behavioral Therapy is the gold standard for treating patients who self -mutilate.
Cutting. Teens are at higher risk for drug use and cutting, as well as other risky behaviors. This kind of acting out is done as a way of communicating what are often very complex feelings about themselves, their world, their future, and in my opinion, DEEPLY conflicted relationships with people in positions of authority.

Related Questions

What is the best treatment for teens who self-harm, more specifically cutting?

Self-harm. Habitual self-harm can be one of features of borderline personality disorder where there is identity diffusion & the act is resorted to in attempt to enlist feeling of temporary relief of discomfort that results from painful traumatic memories. Consult a therapist who specializes with dialectical behavior therapy. Also, treating underlying mood disorder helps. Read more...
Cutting. Teens are at higher risk for drug use and cutting, as well as other risky behaviors. This kind of acting out is done as a way of communicating what are often very complex feelings about themselves, their world, their future, and in my opinion, DEEPLY conflicted relationships with people in positions of authority. Read more...