Oxytocin

Origin and structure

Oxytocin is a peptide hormone of nine amino acids: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly, with an amide at the end. The first six form a ring, closed by a sulphur bridge between the two cysteines, and the last three form a short tail. Its formula is C43H66N12O12S2, with a molecular weight of about 1007. Nerve cells in the hypothalamus make it; it is stored in the posterior lobe of the pituitary gland and released into the blood during labour and when a baby suckles. Vasopressin, the antidiuretic hormone from the same gland that makes the body retain water, differs at only two positions, which is thought to be why large doses of oxytocin also make the kidneys hold on to water.

The name comes from the Greek for 'swift birth'. Vincent du Vigneaud's group worked out its structure and then built it in the laboratory, the first synthesis of a polypeptide hormone; the synthetic molecule proved identical to the natural one, and du Vigneaud received the 1955 Nobel Prize in Chemistry. Medicines contain synthetic oxytocin, which the US label notes is made that way to avoid contamination with vasopressin. They are dosed in international units (IU) rather than milligrams: Syntocinon contains 5 IU per millilitre, Pitocin 10 units per millilitre.

How it works

Oxytocin acts on the oxytocin receptor, which is coupled to G proteins. In the muscle of the uterus, activation releases calcium inside the cells and the muscle contracts, in rhythmic contractions much like those of natural labour. The number of receptors rises sharply during pregnancy and peaks in early labour at term, so the uterus responds far more strongly at the end of pregnancy than earlier, and the response differs a great deal between women. In the breast it makes the cells around the milk glands contract, which pushes the milk out: the let-down reflex.

In the blood it lasts only minutes. The US label gives a half-life of about 1 to 6 minutes, shorter in late pregnancy and during breastfeeding; the Dutch label gives 3 to 20 minutes. The liver and kidneys clear it, helped in pregnancy by oxytocinase, an enzyme that mother and fetus make and that is abundant in the placenta. This is why it is given as a continuous drip during labour, and why contractions fade soon after the drip is stopped.

Oxytocin is also released inside the brain, where it acts as a signalling substance, and animal studies, mostly in rodents, tied it to maternal care and pair bonding. That led researchers to nasal sprays, on the idea that some of the peptide reaches the brain directly through the nose. How much does so in people has not been established; the clinical trials measure behaviour and symptoms, not brain levels.

Is oxytocin approved?

Yes, as a hospital medicine for labour and the hours after birth, in the EU and the US. In the Netherlands and the US its approved uses all concern pregnancy and birth, plus milk let-down in the Netherlands until 2025; none covers social, psychiatric or developmental conditions such as autism, anxiety or PTSD.

In the EU, oxytocin is authorised country by country rather than through the EMA. In the Netherlands the registered medicine is Syntocinon 5 IU/ml solution for injection or infusion (RVG 03714, Alfasigma), prescription-only; a few parallel-imported oxytocin injections of the same strength are registered as well. Until 2025 the Netherlands also had a registered oxytocin nasal spray of 40 IU/ml (RVG 03716, formerly sold as Syntocinon) to help women whose milk does not let down during breastfeeding or pumping; its registration ended on 22 August 2025, and the Farmacotherapeutisch Kompas now lists the spray as a pharmacy-supplied preparation.

Research-grade oxytocin, the peptide sold for laboratory use, is not one of these medicines. It has no marketing authorisation, is not made under a medicines licence, and may not be used in people.

• Netherlands (Syntocinon): inducing labour for medical reasons, such as an overdue pregnancy, early rupture of the membranes or pre-eclampsia; strengthening weak contractions; making the uterus contract when it is closed after a caesarean section; and preventing and treating bleeding and a slack uterus (atony) after birth. For labour it may only be given as an intravenous infusion, never as an injection.
• US (Pitocin and generic oxytocin injections): starting or improving contractions when there is a medical reason, as an add-on in incomplete or inevitable abortion (miscarriage), and producing contractions in the third stage of labour to control bleeding after birth. A boxed notice states that Pitocin is not indicated for elective induction, meaning labour started without a medical reason, because the data are inadequate to weigh benefit against risk. Novartis's Syntocinon injection and the Syntocinon nasal spray are listed as discontinued in Drugs@FDA.

What the research shows

The evidence splits in two. For its approved uses in labour and after birth, oxytocin has decades of hospital experience behind it, and the open questions are about how to dose it rather than whether it works. For everything else, tested mostly with nasal sprays, small early studies looked promising, and the larger, better-controlled trials have largely been negative:

• Labour induction, high versus low dose (Cochrane review 2014): nine trials with 2,391 women. Higher-dose regimens made no significant difference to the share of women without a vaginal birth within 24 hours (risk ratio 0.94) or to the caesarean rate (0.96), but caused more overstimulation of the uterus (risk ratio 1.86, 95% CI 1.55 to 2.25). The trials were at moderate to high risk of bias.
• Autism, SOARS-B (NEJM 2021): 290 children and adolescents aged 3 to 17 received an oxytocin nasal spray (target 48 IU a day) or placebo for 24 weeks. Social withdrawal scores fell by 3.7 points on oxytocin and 3.5 on placebo, a difference of −0.2 (95% CI −1.5 to 1.0); the secondary measures generally did not differ either.
• Autism in adults (Mol Psychiatry 2020): 106 men aged 18 to 48 in Japan received 48 IU a day or placebo for 6 weeks. Both groups improved on the primary measure of social reciprocity, with no significant difference between them, although blood levels of oxytocin did rise on the spray; repetitive behaviour improved more on oxytocin, a secondary outcome.
• Mental disorders overall (Neurosci Biobehav Rev 2026): a meta-analysis of 42 double-blind randomised trials with 1,922 participants, in autism, schizophrenia, substance use and other disorders, found a small and non-significant overall effect (g = 0.17, 95% CI −0.05 to 0.38). Without two outlying substance-use trials the effect shrank to 0.05; analysed by disorder, a small significant effect appeared in schizophrenia (g = 0.12).
• PTSD prevention (Biol Psychiatry 2017): an Amsterdam-led trial gave 120 emergency-department patients with acute distress, most after an accident, oxytocin (40 IU twice a day for 8 days) or placebo, starting within 12 days of the trauma. Clinician-rated PTSD symptoms did not differ at 1.5 months, the primary outcome, or later; in a secondary analysis, people with severe early symptoms did better on oxytocin.
• Trust (Nat Hum Behav 2020): a preregistered replication of the influential 2005 trust-game experiment, designed with more than 95% power, found no effect of oxytocin on trust under the original conditions. Exploratory analyses hinted at an effect only in people with a low disposition to trust, which the authors say still needs confirmation.

Side effects and warnings

When oxytocin is given by drip to start or strengthen labour, the main danger is overstimulation of the uterus: contractions that are too strong or last too long, which can deprive the baby of oxygen and, rarely, tear the uterus. That is why both labels allow it for this purpose only as an intravenous infusion in hospital, with continuous monitoring of the contractions and the baby's heart rate.

The Dutch label lists headache, a fast or slow heart rate, nausea and vomiting as common. Long infusions of high doses together with large volumes of fluid can cause water intoxication, with low blood sodium and seizures; deaths of mothers from it have been reported. A rapid injection straight into a vein can cause a sudden fall in blood pressure with flushing and a fast heartbeat, and can prolong the QT interval of the heart. Anaphylaxis is rare; it has been reported in women with a latex allergy, which may raise the risk.

In the nasal-spray trials the picture is milder. In SOARS-B (24 weeks) and the Japanese trial in adult men (6 weeks), adverse events were no more frequent on oxytocin than on placebo; one man in the Japanese trial developed temporary breast enlargement. For the former Dutch lactation spray, the Kompas lists abnormal uterine contractions as uncommon and allergic skin reactions, nausea and headache as rare, and because the spray can trigger contractions it is contraindicated in pregnancy.

Frequently asked questions

Is oxytocin legal in the Netherlands?

As a medicine, only on prescription. Syntocinon injection (RVG 03714) is prescription-only and is used in hospitals during and just after birth. The nasal spray for milk let-down (RVG 03716, formerly sold as Syntocinon) has not been a registered medicine since 22 August 2025; the Farmacotherapeutisch Kompas lists it as a pharmacy-supplied preparation. Research-grade oxytocin is not a medicine and may not be used in people.

Does an oxytocin nasal spray help with autism?

The large trials say no. In SOARS-B, 290 children and adolescents aged 3 to 17 received oxytocin (target 48 IU a day) or placebo for 24 weeks; social withdrawal scores improved by 3.7 and 3.5 points, a difference that was not significant. A Japanese trial in 106 adult men (48 IU a day for 6 weeks) also found no difference on its primary measure of social reciprocity. Oxytocin is not approved for autism in the Netherlands or the US.

Is oxytocin really the 'love hormone' that makes people more trusting?

The trust idea comes largely from an influential 2005 experiment in which a nasal spray made investors in a trust game hand over more money. Later trust-game studies gave inconclusive results, and a large preregistered replication published in 2020 found no effect under the original conditions. In the body oxytocin clearly matters for birth and breastfeeding, and in animals for bonding, but a spray has not been shown to change how people feel about or trust each other.

Is oxytocin banned in sport?

No. Oxytocin is not named on the WADA Prohibited List for 2026, nor on the Dutch Dopingautoriteit's list of prohibited substances, and because it is an approved medicine, the catch-all class S0 for non-approved substances does not apply. Desmopressin, a synthetic relative of vasopressin, is prohibited as a masking agent, but oxytocin is not.

Is research-grade oxytocin the same as Syntocinon or Pitocin?

No. Syntocinon and Pitocin are sterile solutions with a fixed number of units per millilitre, made and tested under pharmaceutical rules and given in hospital. Research-grade oxytocin is a peptide sold by weight for laboratory use; its identity and purity are what a certificate of analysis says, nothing more, and it may not be used in people. Our lab results show what we test for.

How long does oxytocin stay in the body?

Only minutes. The US label gives a half-life in the blood of about 1 to 6 minutes, the Dutch label 3 to 20 minutes. After an injection into a vein the uterus responds almost at once. After an injection into a muscle, the Dutch label gives an onset within 2 to 4 minutes and an effect lasting 30 to 60 minutes; the US label gives 3 to 5 minutes and 2 to 3 hours.

Storage and handling

Store according to product-label instructions and batch handling notes. Lyophilized research peptides are commonly kept dry, protected from light, and handled with clean laboratory technique.

References

Checked against these sources on 28 October 2026.

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