Acceptance and commitment therapy for psychiatric inpatients diagnosed with depression and insomnia: a multiple-baseline single-case study.

Introduction: The overarching goal of ACT is to increase psychological flexibility, which can be enhanced through mechanisms such as acceptance, valued-driven actions, or mindfulness. Several meta-analyses confirm the effectiveness of Acceptance and Commitment Therapy (ACT) in the treatment of clinical and subclinical populations, including patients diagnosed with depressive disorder and insomnia, largely within outpatient settings. However, there is no scientific research evaluating the efficacy of ACT as an adjunct treatment for psychiatric inpatients with depression. This study aimed to evaluate the efficacy of a manualized ACT treatment in addition to treatment as usual (TAU), within an inpatient setting for patients diagnosed with depressive disorder and comorbid insomnia. Method: Eight psychiatric inpatients received eight ACT sessions (two per week), in addition to TAU, which involved cognitive behavioral therapy (CBT) and psychiatric medication. A single case series design with an A-B replication across inpatients was implemented. Patients were assessed one week (T1) and one day (T2) before ACT treatment (while already receiving TAU), as well as one week (T3) and three months (T4) after treatment termination. Symptom improvement was assessed using self-report questionnaires: Beck Depression Inventory-II (BDI-II), Regensburger Insomnia Scale (RIS), Acceptance and Action Questionnaire-II (AAQ-II), Sleep Problem Acceptance Questionnaire (SPAQ), and quality of life (WHOQOL-BREF). Results: No significant change was observed from T1 to T2 (p >.05). However, significant improvement from T2 to T3 and T2 to T4 was found for depressive symptoms, insomnia, psychological flexibility, acceptance of insomnia symptomatology, and quality of life related to physical and psychological symptoms. Discussion: The findings suggest that ACT is a promising adjunct intervention, applicable transdiagnostically for individuals suffering from depression and comorbid insomnia in inpatient settings. By enhancing psychological flexibility and symptom acceptance, ACT may offer unique benefits beyond traditional CBT, particularly for patients with residual symptoms, chronic distress, or recurrent depressive episodes. Despite these promising findings, results must be interpreted with caution due to the small sample size and lack of a control group. Future research should replicate and extend these findings in larger randomized controlled trials to further evaluate ACT's potential in inpatient psychiatric care.