Oxytocin increases trust in men low in dispositional trust.

In recent years, increasing skepticism regarding oxytocin's (OT) influence on social behavior arose. Low power, HARKing (hypothesizing after the results are known), and replication failures have clouded the field. Here, we directly address these concerns with a high-powered, preregistered study that offers robust evidence for a causal effect of OT on trust among males with a low disposition to trust. We recruited 359 low-trusting men who participated in a trust game with complete anonymity. Results show that OT administration significantly increased trusting behavior by roughly 15%, with consistent effects across regression models with and without controls for personality traits. A pooled data analysis incorporating a previous sample (n = 219) of low-trusting individuals further strengthens this conclusion, yielding a statistically significant 16.9% increase in trust. No interaction effect was found between OT and the degree of dispositional trust, suggesting OT's effect may be uniform across the low-trusting spectrum. These findings present a strong case for OT's selective trust-enhancing role. By isolating OT's impact within a well-defined subpopulation and experimental context, this study resolves a key question in the debate over neurobiological determinants of trust.