Borderline Personality Disorder (BDP) is a serious mental disorder that affects about 1-2% of the general population, and it is characterized by severe psychosocial impairment and a high mortality rate due to suicide. Currently, the most effective treatments for BPD are psychotherapy (cognitive behavior therapy - CBT -) and pharmacotherapy (often as an important adjunctive role, especially for diminution of symptoms such as affective instability, impulsivity, psychotic-like symptoms and self-destructive behavior). Nevertheless, although several drugs are used in these patients, these drugs induce an improvement of some symptoms but do not cause the remission of BPD. Thus, identification of novel treatments is needed.

The objective of this study is to examine the efficacy of Omacor® ( a mixture of omega-3-acid ethyl esters: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) ) for BDP patients receiving CBT. Patients with BDP will be randomly allocated to the three arms of the study: 1- CBT+placebo, 2- CBT+Omacor 1680 mg/d, 3- CBT+Omacor 3360 mg/d. Follow up will last for 12 weeks. Assessment of affective symptoms, impulsivity and aggressivity will be carried out at baseline and at 2, 4, 6, 8, 10 and 12 weeks.

Inclusion Criteria:

1. Meet DSM-IV criteria for BPD assessed by the Structured Clinical Interview for DSM-IV Personality Disorders (SCID-II).
2. Clinical Global Impression of Severity for BDP > 3.
3. Age between 18 and 65 years.
4. Be able to give informed consent for participation.
5. Place of residency compatible with the assistance to the center.
6. If woman, use of effective contraception.

Exclusion Criteria:

1. Have a serious medical illness.
2. History of omacor® allergy.
3. Current diagnostic unipolar depression, bipolar disorder type I, Obsessive-Compulsive Disorder, schizophrenia and other psychotic disorders.
4. DIB-R > 8.
5. Suicidal thinking that requires hospital admission.
6. Meet DSM-IV criteria for alcohol, benzodiazepine, opioid or psychostimulant dependence in the six months prior to trial entry.
7. Transaminase elevation within three times the upper limits of normality.
8. Treatment with stable doses of antidepressants or mood stabilizers for less than six weeks.
9. Treatment with stable doses of antipsychotics for more than 1 week in the last three months.
10. Have received electroconvulsive therapy for the six months prior to trial entry.
11. Have received DBT in the last 12 months prior to trial entry.
12. Are pregnant or nursing.
13. Have participated in any other investigational study in the last 6 months prior to trial entry.
14. Current treatment or expectation to start any treatment with drugs that may interact with the study.