Oxytocin Reactivity to the Therapeutic Encounter as a Biomarker of Change in the Treatment of Depression

Public Significance Statement This study highlights reactivity of the oxytocin system as an important biomarker of success in the treatment of depression. Depression affects millions worldwide, thus underscoring the urgent need to optimize health care practices. To better understand the processes involved in psychotherapy gains, studies have emphasized the need to complement subjective reports with objective measures, in particular biological markers. Oxytocin (OT) has been proposed as a potential biomarker in the treatment of depression given its involvement in depression-related psychological and physiological functions and the formation of close relationships. Here, we assessed whether OT reactivity to therapeutic encounters (absolute and/or directional reactivity) is linked to improvements in depressive symptoms from session to session during psychotherapy. A total of 284 saliva samples were collected from 30 adult clients who underwent 16 sessions of manualized psychodynamic psychotherapy for depression in a university setting. Salivary OT was measured before and after five preselected sessions distributed evenly throughout the therapy. The Beck Depression Inventory-II (BDI-II) was administered at the beginning of each session. Multilevel growth models indicated that clients exhibiting greater absolute OT reactivity showed greater improvement in depressive symptoms throughout treatment. Directional reactivity was not associated with depressive symptom change. In addition, clients with higher baseline OT levels displayed less change in depressive symptoms. These findings highlight reactivity of the OT system, in either direction, as an important feature of the treatment response. Consistent with recent models of the neurobiology of resilience, OT reactivity appears to serve as an important biomarker of psychotherapy gain in the treatment of depression.