Oxytocin nasal spray: why the 'trust hormone' studies didn't replicate

The study that made oxytocin famous

In 2005 a team in Zurich published a short paper in Nature with a striking claim. Men given oxytocin by nasal spray before playing an economic trust game, in which they could hand money to a stranger who might or might not return it, trusted more. The authors wrote that oxytocin caused a substantial increase in trust, that it was not simply a greater willingness to take risks, and that it fitted animal research on oxytocin as a basis for social bonding (randomised trial, small) ¹.

The paper launched a field. Oxytocin became the 'trust hormone' and the 'love hormone' in news coverage, and hundreds of studies followed, testing nasal oxytocin on empathy, generosity, eye contact, emotion recognition, anxiety, autism, schizophrenia and more. Nasal sprays labelled as oxytocin are still sold online for bonding and social confidence.

How the trust finding unravelled

By 2015, a review led by researchers at Caltech concluded that the simplest promising finding, intranasal oxytocin increasing trust, had not replicated well. They also found the blood-level evidence flawed by how oxytocin is measured outside the brain, and large genetic studies failed to find consistent links between oxytocin receptor variants and trust (review) ². Their conclusion: the cumulative evidence did not robustly show that human trust is associated with oxytocin, let alone caused by it.

The decisive tests were registered replications, in which the methods and analysis are fixed and published before the data are collected, so the results cannot be steered afterwards. In 2020 a team ran a large double-blind, placebo-controlled replication with more than 95% statistical power, including the 'minimal social contact' condition of the original. They found no effect of oxytocin on trust in that condition; an exploratory hint in another condition needed confirming (registered replication, 321 people) ³.

A 2026 registered report in Cortex tested 211 more people and then pooled its data with the 2020 study. Neither dataset, nor the combined 532 participants, showed that intranasal oxytocin increases trust, and equivalence testing on the pooled data indicated that any effect is too small to be meaningful (registered report) ⁴.

Why so many oxytocin findings were probably false

Failed replications are common across psychology, and oxytocin research had several reasons to be especially vulnerable. A 2016 analysis in Biological Psychiatry examined the statistical power, prior odds and bias of intranasal oxytocin studies and concluded they were generally underpowered, with a high probability that most published findings do not represent true effects (methods analysis) ⁵.

Underpowered means too few participants to detect a realistic effect. When small studies do find something, the result is more likely to be a fluke or an exaggeration, and journals have historically been more willing to publish positive results than null ones. Add flexible analyses, many possible outcomes, and a theory attractive enough to make everyone hope it is true, and a literature can fill with effects that vanish when someone runs one large, pre-specified test.

Measurement added to the confusion. Many studies correlated oxytocin levels in blood or saliva with behaviour, but the 2015 review found that evidence flawed by how oxytocin is measured in peripheral fluids ². Levels in the blood are also a step removed from the brain, where the social effects are supposed to arise. A correlation built on an unreliable measurement cannot carry much weight, however intuitive the story.

There is also a delivery question. Oxytocin is a peptide, and whether a nasal spray gets meaningful amounts into the human brain has long been debated. A 2019 study in mice found that nasal oxytocin did reach the brain's extracellular fluid, in the amygdala and partly the hippocampus, within 30 minutes (animal evidence) ⁶; that supports the route in principle but does not tell us how much reaches the human brain, or whether it changes behaviour.

Autism: the biggest trial

The highest-stakes claim was that oxytocin could improve social functioning in autism. The authors of the largest trial noted that small studies had suggested a benefit and that oxytocin had already been given to many autistic children in clinical practice. SOARS-B, funded by the US National Institute of Child Health and Human Development, randomised 290 children and adolescents aged 3 to 17 to nasal oxytocin or placebo for 24 weeks. Social withdrawal scores improved by 3.7 points on oxytocin and 3.5 on placebo, a difference of 0.2 (P = 0.61), and secondary outcomes generally did not differ. Side effects were similar in both groups (randomised trial, 290 children) ⁷.

A 2025 follow-up analysis of the same trial looked for what predicted improvement on placebo, noting that placebo responses in autism trials can make real effects harder to detect ⁸. That is a reason to design future trials better, not evidence that oxytocin works.

Mental health conditions more broadly

A 2026 meta-analysis pooled 42 double-blind randomised trials comparing nasal oxytocin with placebo in autism, schizophrenia-spectrum disorders, substance use disorders and other conditions, 1,922 participants in total. The overall effect was small and not statistically significant, with large differences between trials; removing two outlier substance-use studies shrank it further, to almost nothing. A small significant effect remained in schizophrenia-spectrum disorders, and studies with more women showed larger effects, both findings the authors call worth testing properly (meta-analysis) ⁹.

In healthy people, single doses do seem to nudge some laboratory measures. A 2017 meta-analysis of 33 studies found one dose improved recognition of basic emotions, especially fear, and increased the expression of positive emotions in healthy people, but had no significant effect in clinical populations (meta-analysis) ¹⁰. Brain-imaging studies show changes in activity during emotion tasks ¹¹. Small, short-lived shifts on laboratory tasks are a long way from the sprays' marketing.

What oxytocin is approved for, as of October 3, 2026

Oxytocin is a real and important medicine, as an injection. FDA approved Pitocin, an oxytocin injection, for use before and after delivery; its label indicates it for starting or improving contractions when there is a medical reason, and for producing contractions and controlling bleeding after birth. The label's important notice says it is not indicated for elective induction of labour, because the data are inadequate to weigh benefits and risks ¹². Our entry records that intranasal oxytocin is not FDA-approved in the US ¹³.

Obstetric trials show how carefully even the approved use is studied. In one trial of women whose labour had been induced, stopping oxytocin once active labour began lengthened labour by 41 minutes, while continuing it more than doubled fetal heart rate abnormalities (randomised trial) ¹⁴. Across eight trials and 3,154 women, high-dose regimens shortened labour by about an hour without reducing caesarean births (systematic review) ¹⁵. A related long-acting drug, carbetocin, matched oxytocin in preventing bleeding after birth in a large trial (randomised trial) ¹⁶.

For athletes, oxytocin is not on WADA's Prohibited List ¹³.

Questions to ask before buying an oxytocin spray

• What effect is it supposed to have, and has a large, pre-registered trial confirmed it? (For trust and for autism, the largest trials found none.)
• What is actually in the bottle? Nasal oxytocin products sold online are not FDA-approved, and contents and strength are unverified.
• Is the goal something a clinician could help with directly, such as anxiety, social difficulties or a mental health condition?
• If I am pregnant or could be, has a doctor been told? Oxytocin causes uterine contractions; that is what the approved injection is for.

The wider lesson

Oxytocin is a textbook example of how an exciting, plausible, small study can become received wisdom and a consumer product before anyone checks it properly. Many peptides sold online rest on even less: a handful of rodent studies, or human studies never repeated. Our guide to reading a peptide study covers how to tell a robust finding from a fragile one: sample size, pre-registration, independent replication, and whether the outcome is something a person would actually notice.

The bottom line

The idea that a nasal spray of oxytocin makes people more trusting did not survive large, carefully designed replications, and the best autism trial found no benefit. Single doses may shift some laboratory measures of emotion in healthy people, and a small signal in schizophrenia is worth a proper trial. Oxytocin's proven role is obstetric, as a prescription injection. A spray bought online for bonding or confidence is selling a finding the science has largely withdrawn.

Frequently asked questions

Does oxytocin nasal spray increase trust?

The 2005 study that reported it did not replicate. A 2020 registered replication of 321 people and a 2026 pooled analysis of 532 found no meaningful effect on trust.

Does oxytocin help autism?

In the largest trial, 290 children and adolescents, 24 weeks of nasal oxytocin did no better than placebo on social withdrawal or secondary measures.

What are the benefits of oxytocin?

Its proven benefit is obstetric: as the injection Pitocin it is approved to start or strengthen contractions and to control bleeding after birth. Benefits of nasal sprays for mood or relationships are not established.

Is oxytocin nasal spray FDA-approved?

No. As of October 3, 2026, intranasal oxytocin is not FDA-approved in the US; only the injection is.

Why did the oxytocin studies fail to replicate?

A 2016 analysis found most intranasal oxytocin studies were too small, giving a high probability that many published findings were false positives. Larger pre-registered studies did not confirm them.

Related on Grey Peptides

• Oxytocin
• How to read a peptide study
• Carbetocin

Sources

1. Kosfeld, M., et al. (2005). Oxytocin increases trust in humans. Nature, 435(7042), 673-6. PMID: 15931222
2. Nave, G., et al. (2015). Does Oxytocin Increase Trust in Humans? A Critical Review of Research. Perspect Psychol Sci, 10(6), 772-89. PMID: 26581735
3. Declerck, C. H., et al. (2020). A registered replication study on oxytocin and trust. Nat Hum Behav, 4(6), 646-655. PMID: 32514040
4. Kroll, C. F., et al. (2026). Absence of a meaningful effect of intranasal oxytocin on trusting behavior: a registered report with pooled equivalence testing. Cortex, 198, 208-233. PMID: 41880977
5. Walum, H., et al. (2016). Statistical and Methodological Considerations for the Interpretation of Intranasal Oxytocin Studies. Biol Psychiatry, 79(3), 251-7. PMID: 26210057
6. Smith, A. S., et al. (2019). Oxytocin delivered nasally or intraperitoneally reaches the brain and plasma of normal and oxytocin knockout mice. Pharmacol Res, 146, 104324. PMID: 31238093
7. Sikich, L., et al. (2021). Intranasal Oxytocin in Children and Adolescents with Autism Spectrum Disorder. N Engl J Med, 385(16), 1462-1473. PMID: 34644471
8. Verdes, A., et al. (2025). Predictors of Placebo Response in the Study of Oxytocin in Autism to Improve Reciprocal Social Behaviors. J Child Adolesc Psychopharmacol, 35(4), 202-210. PMID: 39970017
9. Bonnieux, J., et al. (2026). Does intranasal oxytocin reduce symptoms of mental disorders? A meta-analysis of clinical trials. Neurosci Biobehav Rev, 187, 106749. PMID: 42134427
10. Leppanen, J., et al. (2017). Meta-analysis of the effects of intranasal oxytocin on interpretation and expression of emotions. Neurosci Biobehav Rev, 78, 125-144. PMID: 28467893
11. Grace, S. A., et al. (2018). Oxytocin and brain activity in humans: A systematic review and coordinate-based meta-analysis of functional MRI studies. Psychoneuroendocrinology, 96, 6-24. PMID: 29879563
12. Par Health USA. PITOCIN (oxytocin injection, USP) prescribing information, Indications and Usage and Important Notice. DailyMed version 15, effective May 5, 2026; read October 1, 2026.
13. Grey Peptides encyclopedia entry for oxytocin: FDA status (Pitocin NDA 018261; intranasal oxytocin not FDA-approved in the US), WADA status (not listed). Read October 3, 2026.
14. Bor, P., et al. (2016). Continuation versus discontinuation of oxytocin infusion during the active phase of labour: a randomised controlled trial. BJOG, 123(1), 129-35. PMID: 26309128
15. Aboshama, R. A., et al. (2021). High dose vs. low dose oxytocin for labor augmentation: a systematic review and meta-analysis of randomized controlled trials. J Perinat Med, 49(2), 178-190. PMID: 32950965
16. Widmer, M., et al. (2018). Heat-Stable Carbetocin versus Oxytocin to Prevent Hemorrhage after Vaginal Birth. N Engl J Med, 379(8), 743-752. PMID: 29949473

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.