Biological modulators of treatment outcome during psychiatric care: The interplay between inflammation and oxytocin

Background: Although scientific advancements highlight the involvement of inflammatory processes in psychiatric disorders, few studies have explored how these processes relate to treatment outcomes. This study aimed to examine whether inflammation is associated with reduced treatment outcomes in inpatient psychiatric care, and whether oxytocin (OT)—a neuropeptide known for its anti-inflammatory properties—may buffer these effects. Methods: Patients (N = 72; 76% female) who received intranasal OT or placebo twice daily for four weeks, adjunctive to standard inpatient care, were assessed for pre-treatment inflammation using the neutrophil-to-lymphocyte ratio (NLR). Baseline depressive symptoms, anxiety, suicidal ideation, and distress were evaluated through self-report measures at pre- and post-treatment. Multilevel models were used to test the predictive effects of baseline NLR on treatment outcomes and its interaction with OT administration. Results: Higher pre-treatment NLR was associated with reduced improvement in trait anxiety (p = .02). A significant NLR × OT interaction emerged for depression (p = .005), indicating that OT administration did not significantly improve depression outcomes among patients with high baseline NLR (p = .35), whereas it was associated with greater improvement among patients with low baseline NLR compared to placebo (p = .001). Conclusions: Inflammation may represent a biological factor influencing treatment outcomes; however, OT administration appears to benefit primarily patients with low levels of inflammation. Further studies are needed to determine whether other anti-inflammatory agents may mitigate these effects.