The synergistic effects of acute stress and exogenous oxytocin on males’ decision-making under unfairness

Oxytocin (OXT) plays a critical role in stress-induced affiliative behavior, with important implications for socio-economic decision-making. In this study, 95 healthy young males were randomly assigned to four groups, receiving either 32 IU of exogenous OXT or a placebo (PBO) before undergoing the Trier Social Stress Test (TSST) or a control procedure, followed by participation in the Ultimatum Game (UG) as responders, allocating ¥50. The results indicated that OXT inhibited the hypothalamic-pituitary-adrenal (HPA) axis stress response, enhanced sympathetic nervous system activity, and increased subjectively perceived stress. Stress and OXT acted synergistically, reducing males’ acceptance of extremely unfair allocations (¥5) and amplifying the impact of previous offers on expectations, highlighting the salience of social cues after stress exposure and OXT treatment. Cross-project analyses compared OXT- and PBO-treated males with untreated females from a homogeneous study. Males rejected more moderately unfair allocations (¥20, ¥15, ¥10) and exhibited higher disadvantage inequality aversion than females, regardless of OXT treatment. These findings reveal the combined influence of OXT and acute psychosocial stress on males’ decision-making and psychological processes in unfairness contexts, highlighting the biological, psychological, and social dimensions of social behavior.