Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Borderline personality disorder is a severe mental disorder, which has a substantial impact on the lives of patients and those around them. A variety of psychological therapies have been tried and, in May 2020, the latest evidence on these was brought together in a Cochrane Review. We asked one of the authors, Mie Sedoc Jørgensen from Region Zealand Psychiatry in Denmark, to tell us what it shows.

Mie: Borderline personality disorder, or BPD, is a severe mental disorder. Some of its most defining features are emotion dysregulation, impulsivity, anger, repeated self-injury and chronic suicidal tendencies, together with feelings of emptiness and fear of abandonment. People with BPD also have severe difficulties in achieving and maintaining vocational and social functioning and about three-quarters of them will present to medical healthcare settings. 
A broad range of psychotherapies exist for BPD. These therapies are typically delivered in individual or group formats, or a combination. The most commonly used are dialectical behavior therapy, mentalization-based treatment, transference-focused therapy, cognitive-analytic therapy, schema-focused therapy and systems training for emotional predictability and problem-solving.
In the current review, we aimed to provide a systematic summary of the evidence from randomized trials of all types of psychotherapy. We hope that this will help people with BPD, their families and friends, mental healthcare workers and policy and decision managers in general, to make informed decisions about evidence-based treatments.
We included randomized trials that had compared psychological therapies against standard control interventions or other specific psychotherapeutic treatments for people with a formal diagnosis of BPD. We were particularly interested in the effects on BPD symptom severity, self-harm, suicide-related outcomes and psychosocial functioning. We also included a set of secondary outcomes to look at specific symptoms such as anger, chronic feelings of emptiness, fears of abandonment and depression, as well as adverse effects.
There is a large amount of literature available on BPD and we had to screen more than 18,000 titles and abstracts and check 400 full-text reports for eligibility. From these, we included 282 reports which provided information on 75 randomised trials that had recruited a total of just over 4500 participants with BPD. All the trials had a high risk of bias, and for most outcomes, we considered the data to be of low quality due to imprecision, small sample sizes and inconsistency.  
However, with these cautions in mind, we found that there were beneficial effects of psychotherapy compared to treatment as usual for all the primary outcomes, although the improvement was clinically important just for BPD severity. This means that BPD-tailored psychotherapies may be more effective than usual treatments, but there is still a need for further high-quality randomized trials with larger sample sizes and greater efforts to limit the risk of bias – especially allegiance bias. It would also help if these trials were more aligned in their use of outcomes, and if the control interventions were standardized in order to give a clear picture of what the psychological therapies are being compared to. Lastly, these trials should have long enough follow-up to establish the long-term effectiveness of treatments for a condition as severe as BPD.

Monaz: If you would like to learn more about the trials that have been done and watch for future updates of this review if the new trials are done, you can find the review online. Go to Cochrane Library dot com and search 'psychological therapies and borderline personality disorder' to see the link to it.