For more than two decades, oxytocin has been associated with the chemistry of social connection, but its effects on human trust have remained surprisingly difficult to pin down. A new randomized study now reports what researchers describe as robust evidence that intranasal oxytocin can increase trusting behavior—but only in a specific group: men who already show a relatively low tendency to trust others. The finding challenges the popular idea that oxytocin simply makes everyone more cooperative or open-minded, suggesting instead that the hormone’s social effects depend heavily on a person’s psychological starting point.
Oxytocin is produced naturally in the body and acts both as a hormone and as a neurotransmitter. It is involved in childbirth and breastfeeding, but it also influences brain systems involved in social evaluation, emotional salience and interpersonal behavior. In 2005, a team led by University of Zurich economist Ernst Fehr reported in Nature that intranasally administered oxytocin increased trusting decisions in a laboratory investment game. That result attracted widespread attention, yet later experiments produced mixed outcomes, with some studies replicating the effect and others finding no general increase in trust.
The uncertainty was amplified by methodological differences across the field. Many earlier experiments included relatively small samples, used different versions of trust tasks or measured psychological traits in inconsistent ways. Researchers also faced concerns about hypotheses being formulated after results were observed, a practice that can make apparently striking findings less reliable. Against this background, Fehr and colleagues designed a study with a larger sample and a hypothesis specified in advance: oxytocin would selectively increase trust among men with a low dispositional tendency to trust.
The international research team recruited 359 men who had first completed a questionnaire measuring their general disposition to trust. Participants identified as having relatively low trust scores were then randomly assigned to receive either oxytocin or an inactive placebo through the nose. Intranasal delivery is commonly used in laboratory studies because it is intended to allow the compound to reach the brain without the need for an injection, although the precise pathways and central effects of this method remain an active area of scientific debate. Neither the participants nor the researchers conducting the behavioral testing knew which treatment each man had received.
After treatment, the men played an anonymous trust game involving real money. Each participant began with an endowment of 12 euros and was placed in the role of an investor. He could transfer 0, 4, 8 or 12 euros to an unknown counterpart. The transferred amount was tripled, after which the trustee could return any amount. The investor’s decision therefore involved a calculated risk: transferring more money created a greater potential return, but also increased the amount that could be kept by the other player. In this setting, the amount sent serves as a behavioral measure of trust rather than a simple verbal statement of confidence.
Men in the low-trust group who received oxytocin transferred approximately 15 percent more money than comparable men who received the placebo. To strengthen the analysis, the researchers combined their results with data from an earlier comparable experiment, creating a pooled sample of 578 men with low dispositional trust. Across the combined dataset, oxytocin was associated with an increase of nearly 17 percent in trusting behavior. The relationship remained after the researchers statistically controlled for different personality characteristics, indicating that the result was not easily explained by broad differences in traits such as sociability or risk tolerance.
The effect was not observed as a universal shift toward trust. Within the selected low-trust group, men with the very lowest scores did not respond more strongly than men whose scores were somewhat higher but still fell within the low-trust range. This pattern suggests that oxytocin may act less like a general “trust drug” and more like a context-sensitive regulator of social expectations. Its influence may become visible when an individual begins with skepticism or caution, while producing little measurable change in people who are already relatively trusting.
The biological explanation remains unresolved. One possibility is that oxytocin increases the expectation that another person will cooperate, making a risky transfer appear more worthwhile. Another is that it reduces the perceived threat of betrayal or softens the emotional cost associated with being cheated. These possibilities are not interchangeable: raising expectations about cooperation would directly alter judgments about another person’s likely behavior, whereas reducing fear could change the emotional weight of the same risk without changing the underlying prediction. The study measured decisions, not brain activity or hormone signaling, so it cannot determine which mechanism is responsible.
The researchers deliberately restricted the experiment to men to make its results more directly comparable with previous oxytocin studies. That choice also leaves an important question unanswered: whether the same selective effect occurs in women. Future experiments will need to examine sex differences, individual personality profiles, dosage, social context and the reliability of intranasal oxytocin’s effects across laboratories. For now, the study offers a more precise message than the familiar claim that oxytocin makes people trust more. In men who are naturally reluctant to trust, the hormone appears capable of shifting behavior toward greater confidence in an anonymous partner—but its power is selective, conditional and rooted in a social decision rather than a simple chemical switch.
Subject of Research: People
Article Title: Oxytocin increases trust in men low in dispositional trust.
News Publication Date: 11 August 2026
Web References: https://doi.org/10.1073/pnas.2602655123
References: Bodo Vogt, Paul Bengart, Carolyn Declerck and Ernst Fehr. “Oxytocin increases trust in men low in dispositional trust.” Proceedings of the National Academy of Sciences, 11 August 2026. DOI: 10.1073/pnas.2602655123.
Keywords: Oxytocin, trust, behavioral economics, social behavior, neuroscience, hormones, randomized controlled trial, intranasal oxytocin, human behavior, decision-making
