Background: In bipolar spectrum disorder, some individuals experience ongoing, frequent fluctuations in mood outside of affective episodes. There are currently no evidence-based psychological interventions designed to address this. This feasibility study is a phase II evaluation of a dialectical behavioural therapy-informed approach (Therapy for Inter-episode mood Variability in Bipolar [ThrIVe-B]). It seeks to examine the feasibility and acceptability of a future definitive trial evaluating the clinical and cost effectiveness of the ThrIVe-B programme.

Methods/design: Patients will be randomised 1:1 to either treatment as usual only (control arm) or the ThrIVe-B intervention plus treatment as usual (intervention arm). Follow-up points will be at 3, 6, 9 and 15 months after baseline, with 9 months as the primary end point for the candidate primary outcome measures. We aim to recruit 48 individuals meeting diagnostic criteria for a bipolar spectrum disorder and reporting frequent mood swings outside of acute episodes, through primary and secondary care services and self-referral. To evaluate feasibility and acceptability, we will examine recruitment and retention rates, completion rates for study measures and feedback from participants on their experience of study participation and therapy.

Discussion: Proceeding to a definitive trial will be indicated if the following criteria are met: (1) trial participation does not lead to serious negative consequences for our participants; (2) any serious concerns about the acceptability and feasibility of the trial procedures can be rectified prior to a definitive trial; (3) follow-up data at 9 months are available for at least 60% of participants; (4) at least 60% of patients in the ThrIVe-B arm complete treatment.

Trial registration: ISRCTN, ISRCTN54234300. Registered on 20 July 2017. © 2018 The Author(s).