Bipolar Disorders (BD) typically involve repeated episodes of both depression and excessively high mood or irritability (hypomania or mania). BD presents considerable challenges for the individual, his or her supporters, and society more generally. Medication is generally considered to be the mainstay treatment, however a substantial number of individuals with BD continue to experience episodes despite use of medication. Furthermore, ongoing mood instability either outside of episodes, or as the main feature of their BD, is a significant difficulty experienced by many. Whilst studies suggest that certain psychological therapies can be helpful for people experiencing full bipolar episodes, or to reduce risk of future episodes, there are no evidencebased psychological therapies available for individuals experiencing ongoing mood instability. Dialectical Behaviour Therapy (DBT) was developed several decades ago as an approach for people with Borderline Personality Disorder. DBT aims to give individuals who experience rapid and intense shifts in affect skills for managing this. Despite the many similarities in the symptoms experienced by individuals with Borderline Personality Disorder and those with Bipolar Disorder only a small number of studies have tested DBT for BD, and no studies to date have specifically investigated DBT as a means to help individuals with ongoing mood instability. We have developed a version of groupbased DBT that draws upon our own research to adapt standard DBT for this client group (DBTBD).

The group is designed to be delivered efficiently within the U.K. healthcare system whilst meeting the needs of individual participants through use of additional individual sessions and a mobile phone application. The current study investigates how acceptable DBTBD is to clinicians and patients, and whether - for the small number of individuals in the study -changes in symptoms and key ways of thinking and behaving appear to take place across the period of treatment.

Inclusion criteria for patient participants are: i) aged 18 or over; i) meets DSMV criteria for Bipolar Spectrum Disorder; iii) current bipolar mood instability (over the past two years numerous periods with hypomanic symptoms that do not meet criteria for a hypomanic episode and numerous periods with depressive symptoms that do not meet criteria for a depressive episode, continuing into the past month); iv) client wishes to engage in psychological therapy that focusses primarily on ongoing mood instability and its consequences.

Exclusion criteria are: i) current substance dependence disorder; ii) currently receiving other psychological therapy; iii) the patient is currently actively suicidal; iv) presenting difficulties that are characteristic of Borderline Personality Disorder rather than Bipolar Disorder and that would be an early treatment target in standard DBT (frequent and serious deliberate selfharm, marked disturbance in ability to form or maintain interpersonal relationships); v) presence of another area of difficulty that the therapist and client believe should be the primary focus of intervention (for example panic disorder with agoraphobia, Post Traumatic Stress Disorder); vi) the information available suggests that the person may present a significant risk to other group members (such as aggression, likelihood of carrying out sexual or other exploitation); vii) the person lacks capacity to consent to treatment or research participation; viii) currently experiencing an episode of mania.

Individuals with frequent bipolar mood swings.

Data would potentially be shared on Open Repository Exeter (University of Exeter's open data repository)