Back in 2005, a groundbreaking study from the University of Zurich suggested that oxytocin, a hormone known for shaping social interactions, could make people more trusting. In a controlled experiment, giving oxytocin by nasal spray increased the amount of money that participants were willing to put in the hands of strangers. The finding sparked excitement and controversy.
In subsequent years, follow-up studies showed mixed results. Some supported the effect; others opposed it. Critics highlighted small sample sizes, inconsistent methods, and post hoc hypothesis formation. The question, however, remained: to what extent does oxytocin indeed help turn up the dial on trust, and when?
An international team led by Ernst Fehr (University of Zurich), Bodo Vogt and Paul Bengart (Otto von Guericke University Magdeburg), and Carolyn Declerck (University of Antwerp) has now provided the most robust evidence yet.
359 men with a low trust disposition were recruited. Participants received either oxytocin or a placebo. They then played a trust game, deciding how much money to entrust to an anonymous partner.
Study shows how oxytocin helps the mind modulate social stimuli
The results: men with a low trust disposition who received oxytocin entrusted about 15% more money than those given a placebo. When combined with earlier data, the pooled analysis of 578 men showed an almost 17% increase in trusting behavior.
“After more than 20 years, we have now succeeded in providing robust evidence of a selective effect of oxytocin,” Fehr said.
The study makes clear that oxytocin doesn’t make everyone more trusting. Instead, it selectively increases trust in men who already score low on trust disposition. Interestingly, the degree of low trust didn’t matter; men with very low scores were affected just as much as those with moderately low scores.
Why does oxytocin have this selective effect? The biological mechanisms remain unclear.
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“The hormone may intensify the expectation that others will cooperate,” Fehr explained. He added that oxytocin may also reduce the fear of being cheated.
Future studies will explore these mechanisms and whether the findings extend to women.
Trust is the glue of social life, influencing cooperation, relationships, and even economic systems. Understanding how oxytocin shapes trust could open doors to new therapies for social disorders, or deepen our grasp of human behavior.
This study doesn’t claim oxytocin is a universal “trust drug.” Instead, it shows that in specific groups- men with a low-trust disposition- oxytocin can reliably shift behavior. After two decades of debate, the hormone’s role in trust is finally coming into sharper focus.
Journal Reference:
- Bodo Vogt, Paul Bengart, Carolyn Declerck, Ernst Fehr. Oxytocin increases trust in men low in dispositional trust. PNAS. 11 August, 2026. DOI: 10.1073/pnas.2602655123
