Is the “social hormone” oxytocin relevant to psychotherapy treatment outcomes? A systematic review of observational and experimental studies

Background: Oxytocin, popularly known as the “social hormone”, has wide implications for the regulation of socially relevant cognitions, emotions and behaviors. Individual differences in oxytocin may be relevant to mental health treatment outcomes, given the centrality of the therapeutic relationship in psychotherapy. Methods: This systematic review aimed to synthesize findings from psychotherapy studies that examined oxytocin measurement and augmentation methods and their association with treatment outcomes. The methodology was preregistered in the Open Science Framework (https://osf.io/xtyvc/?view_only=2bc37dc0b2cd41f8939e2964bd8b884f). Five databases were searched on 30th of March 2023 (PubMed, SCOPUS, Web of Science, Medline, PsycINFO). Eligible studies were assessed for risk of bias and findings were summarized using narrative synthesis and vote counting methods. Results: Overall, 24 studies (n=881 participants) including experimental and observational designs and covering various diagnostic groups were reviewed. Findings from 9 studies (n=406) indicate that oxytocin measures were associated with psychotherapy treatment outcomes for depression, and oxytocin-augmentation improved depression outcomes. Results regarding other mental disorders were mixed and inconclusive. Discussion: Current evidence indicates that oxytocin-augmented psychotherapy for depression warrants further research. Currently there is not sufficient evidence to draw firm conclusions regarding the clinical relevance of oxytocin in the context of other disorders. Key limitations are the lack of meta-analytic synthesis and small sample sizes for primary studies.