Emotional instability, impulsivity, ongoing self-harm, frequent suicidal crises, interpersonal problems, substance use disorder, cognitive distortions, and severe internal pain are seen in patients with emotionally unstable personality traits. This is a patient group that requires lot of resources over time, with variable effect. We see a great need for interventions that can help reduce individual suffering and socio-economic challenges and prevent fatigue in the help system. Horse-assisted therapy (HAT) is an innovative complementary approach to psychotherapy. HAT is a sought-after and attractive offer, we shall investigate why and how this can contribute in a well-known method-based psychotherapeutic intervention, Dialectical Behaviour Therapy (DBT) for emotionally unstable adolescents. We shall investigate whether this contributes to symptom reduction, increased experience of social support, treatment retention, strengthened socio-relational function and improved quality of life.