The purpose of the study was to determine whether mindfulness training could be more effective than another active intervention in reducing borderline personality disorder (BPD) symptoms. The main hypothesis was that patients allocated to the mindfulness group would show a greater improvement on global BPD symptomatology. As a second objective, we explored some of the possible underlying mechanisms of both active treatments. For that purpose, changes in decentering, mindfulness facets and cognitive processing of social interactions were also evaluated.

The present study aimed at evaluating the efficacy of mindfulness skills (M) versus interpersonal effectiveness skills (IE) on borderline symptoms. For that purpose, a randomized, active-controlled clinical trial was designed. 64 participants with borderline personality disorder (BPD) diagnosis were allocated to mindfulness (n=32) or interpersonal effectiveness skills (n=32). Both interventions were delivered over a 10-week period. The borderline symptom list (BSL-23) was elected as the primary outcome measure. Mindfulness related capacities, decentering and cognitive processing of social interactions were also evaluated with the Five Facet Mindfulness Questionnaire (FFMQ), the Experiences Questionnaire (EQ) and the Multidimensional Scale of Social Expression (EMES-C), respectively. Assessments were conducted pre and post interventions.

Inclusion criteria:

• Ages between 18 and 45 years
• BPD criteria according to two diagnostic interviews (SCID-II and DIB-R)

Exclusion Criteria:

• Lifetime diagnosis of schizophrenia, drug-induced psychosis, organic brain syndrome, bipolar disorder or mental retardation
• Participating in any sort of psychotherapy during the study or having participated in dialectical behavioral therapy groups in the past