Bipolar Disorder (BD) involves recurrent episodes of mania/hypomania and depression, causing significant impairment in quality of life, functioning, and sleep. Although Psychoeducation, Cognitive Behavioral Therapy, and Family-Focused Therapy show efficacy, especially for recurrence of new episodes, novel interventions targeting bipolar depression and subthreshold symptoms remain necessary. Acceptance and Commitment Therapy (ACT), with effectiveness demonstrated across multiple psychiatric disorders, may improve depressive symptoms, quality of life, and functioning in BD.

This study examines ACT’s impact as a stand-alone intervention, alongside usual pharmacotherapy, on depressive symptoms in BD. Additional targets include quality of life, functioning, sleep quality, and psychological flexibility.

This randomized controlled trial will compare ACT plus usual treatment to usual treatment alone in adults aged 18–65 years with BD, experiencing a current depressive episode or subthreshold depression. The ACT group will undergo 12 weekly sessions. Measurements (baseline, post, 6, 9 and 12 months) will encompass depression symptoms (primary outcome), and functioning, quality of life, sleep quality, and psychological flexibility as secondaries. Analyses using linear mixed models or generalized estimating equations (GEE) will assess group differences over time.

If ACT reduces depressive symptoms and improves related outcomes, it could serve as a valuable adjunct treatment min BD management. This protocol describes the study framework, assessment tools, and intervention approach, expanding understanding of strategies for addressing depressive phases and subthreshold symptoms in BD.