Oxytocin
The hormone behind labour and milk let-down, and the standard drug for starting labour and preventing bleeding after birth
Oxytocin is a nine-amino-acid hormone made in the hypothalamus that contracts the uterus and releases breast milk. As an injected drug, sold in the US as Pitocin, it is used to induce or strengthen labour and to prevent and treat bleeding after birth. It acts within minutes and is cleared within minutes, which is why it is given by infusion. Intranasal oxytocin has been studied for autism and social behaviour with mostly disappointing results, and it is not approved in the US.
What is it?
Oxytocin is a nine-amino-acid hormone made in the hypothalamus and released from the pituitary during labour and breastfeeding. Given as a drug, it makes the uterus contract. According to the Pitocin label, it works by raising calcium inside uterine muscle cells, whose oxytocin receptors multiply during pregnancy and peak in early labour at term. Its plasma half-life is about 1 to 6 minutes, shorter late in pregnancy; an intravenous dose acts almost at once and wears off within an hour, and an intramuscular injection acts within 3 to 5 minutes and lasts 2 to 3 hours. It differs from vasopressin at only two positions, which is why large doses can raise blood pressure and retain water.
The label is unusually cautious about when to use it. A notice at the top says Pitocin is not indicated for elective induction, because the data are inadequate to weigh benefit against risk. It is indicated to induce labour when there is a medical reason (such as preeclampsia, maternal diabetes or ruptured membranes), to strengthen weak labour, as an adjunct in incomplete or inevitable abortion, and after delivery to contract the uterus and control bleeding. For induction it is given only by controlled intravenous infusion in hospital, starting at 0.5 to 1 milliunit a minute and rising by 1 to 2 milliunits every 30 to 60 minutes; the label notes that rates above 9 to 10 milliunits a minute are rarely needed at term.
Its central role is preventing bleeding after birth. In the largest trial of the question, nearly 30,000 women were given oxytocin or heat-stable carbetocin after vaginal birth; blood loss of 500 mL or more, or extra drugs, occurred in 14.4% against 14.5%, so carbetocin was non-inferior, which matters where oxytocin cannot be kept cold. At planned caesarean delivery, a 2025 trial found similar blood loss and no difference in heart-muscle injury markers, but more women needed rescue drugs after oxytocin (46.4%) than after carbetocin (27.2%).
How much to give during labour is a trade-off rather than a settled dose. A meta-analysis of eight trials and 3,154 women found high-dose augmentation shortened labour by about an hour without reducing caesarean delivery, while low doses caused less uterine hyperstimulation; a 140-woman trial found no difference in time to delivery between doses in either lean or obese women.
Whether to keep the infusion running once labour is established has been tested twice. In CONDISOX, 1,200 women with induced labour were randomised in active labour: stopping oxytocin left the caesarean rate statistically unchanged (16.6% against 14.2%) but cut uterine hyperstimulation (3.7% against 12.9%) and abnormal fetal heart patterns (27.9% against 40.8%), at the cost of a longer labour (median 282 against 201 minutes). An earlier, smaller trial found the same pattern.
Outside the delivery room the evidence is weak. The largest test of intranasal oxytocin for autism, a 290-child, 24-week trial published in the New England Journal of Medicine, found no difference from placebo in social or cognitive functioning. In a Prader-Willi syndrome trial, hyperphagia improved more on placebo, and a trial of chronic use in autistic children found no significant effect on face processing. Intranasal oxytocin is not approved in the US.
Its risks come from its potency. Too much makes the uterus contract too hard or too often, which can distress the baby; the label tells staff to stop the infusion at once if that happens, and the effect fades quickly. Prolonged high-dose infusion can cause water intoxication because of its antidiuretic action, and severe high blood pressure has been reported when it was given a few hours after a vasoconstrictor with caudal anaesthesia.
Mechanism of Action
Oxytocin binds the oxytocin receptor on uterine muscle and raises calcium inside the cells, which drives contraction; receptor numbers rise through pregnancy, so the same dose acts more strongly near term.
Uterine contraction
Raising intracellular calcium activates the contractile machinery of uterine muscle (label); this is what starts or strengthens labour and clamps down bleeding vessels after birth.
Receptors rise in pregnancy
Oxytocin receptors in the uterus increase greatly during pregnancy and peak in early labour at term, so before term a higher infusion rate may be needed (label).
Vasopressin-like effects
Because it differs from vasopressin at only two amino acids, large doses can raise blood pressure and retain water (label), the basis of the water-intoxication warning.
Published Research
The studies behind oxytocin, read from their PubMed abstracts: preventing bleeding after birth, dosing and stopping during labour, and the intranasal trials.
Oxytocin vs heat-stable carbetocin: 29,645 women
Blood loss of at least 500 ml or extra uterotonic use occurred in 14.4% on oxytocin and 14.5% on carbetocin, meeting non-inferiority; for blood loss of at least 1,000 ml, non-inferiority could not be shown.
Oxytocin or carbetocin at planned caesarean, 215 women
No difference in troponin rise or estimated blood loss (395 against 335 mL); rescue uterotonics were used after 46.4% of oxytocin and 27.2% of carbetocin deliveries, and total costs were similar.
CONDISOX: stopping the infusion in active labour, 1,200 women
Caesarean delivery occurred in 16.6% after discontinuation and 14.2% with continuation (relative risk 1.17, not significant); stopping cut hyperstimulation (3.7% against 12.9%) and abnormal fetal heart patterns (27.9% against 40.8%) but lengthened labour (282 against 201 minutes).
Stopping vs continuing the infusion in active labour
Stopping oxytocin lengthened active labour by 41 minutes, while continuing it more than doubled fetal heart rate abnormalities (51% vs 20%) and increased uterine hyperstimulation (12% vs 2%).
High vs low dose for augmenting labour
Across 8 randomised trials and 3,154 women, high doses shortened labour by about an hour but did not reduce caesarean delivery; low doses caused less uterine hyperstimulation and tachysystole.
High against low dose in lean and obese women, 140 women
Time to vaginal delivery did not differ between high and low doses in either the lean or the obese stratum, nor did caesarean rates or postpartum haemorrhage.
Intranasal oxytocin in autism: 290 children, 24 weeks
The primary social-withdrawal score fell by 3.7 on oxytocin and 3.5 on placebo (difference −0.2, P=0.61); secondary outcomes and adverse events did not differ.
Intranasal oxytocin in Prader-Willi syndrome
In this randomised trial in children, hyperphagia and repetitive behaviours fell over time on placebo but not on oxytocin.
Chronic intranasal oxytocin in autistic children
The trial found no significant treatment effect on neural face processing; changes favouring oxytocin appeared only in exploratory analyses uncorrected for multiple comparisons.
Dosing Data
In labour oxytocin is given only by controlled intravenous infusion in hospital, started low and increased to the uterine response; after birth it may be added to an infusion or injected into muscle.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. 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. Full medical disclaimer.
Side Effects & Contraindications
Reported Side Effects
From the trials above and the Pitocin prescribing information (Par Health; DailyMed set 6e5a66fc, version 15, effective May 5, 2026).
Contraindications & Cautions
From the label; a clinician decides.
Legal Status
Oxytocin injection is an FDA-approved prescription drug used in hospitals.
Frequently Asked Questions
?What is oxytocin used for?
As an injected drug it starts or strengthens labour and prevents or treats bleeding after birth. It is given in hospital, usually by controlled infusion.
?Does intranasal oxytocin help autism?
The controlled trials cited here found no clear benefit, and it is not FDA-approved for autism or any other use as a nasal spray.
?How long does oxytocin last?
Its plasma half-life is about 1 to 6 minutes. An intravenous dose acts at once and fades within an hour; an intramuscular dose lasts 2 to 3 hours.
?Can Pitocin be used for an elective induction?
The label says no: Pitocin is not indicated for elective induction of labour, because the available data are inadequate to weigh its benefits against its risks.
?Should the drip be stopped once labour is under way?
In the 1,200-woman CONDISOX trial, stopping it in active labour did not significantly change the caesarean rate but cut uterine hyperstimulation and abnormal fetal heart patterns, at the cost of a longer labour.
?Is carbetocin better than oxytocin?
After vaginal birth they worked about equally in a 29,645-woman trial. At planned caesarean, carbetocin needed fewer rescue drugs in a 215-woman trial, with similar blood loss.
?What dose is used after delivery?
The label allows 10 to 40 units added to a running intravenous infusion (no more than 40 units per litre), or 10 units intramuscularly after the placenta is delivered.
References
- [fda-pi] Par Health. PITOCIN (oxytocin injection), US prescribing information: contraindications, adverse reactions and clinical pharmacology (plasma half-life about 1 to 6 minutes). DailyMed version effective May 5, 2026; read September 30, 2026.
- [fda] FDA. Drugs@FDA (openFDA): PITOCIN, NDA 018261, current application approved November 19, 1980. Read September 30, 2026.
- [pubmed] Widmer M, et al. "Heat-Stable Carbetocin versus Oxytocin to Prevent Hemorrhage after Vaginal Birth." N Engl J Med, 2018;379(8):743-752. PMID: 29949473.
- [pubmed] Bekkenes ME, et al. "Effects of Prophylactic Oxytocin or Carbetocin on Troponin Release and Postpartum Haemorrhage at Planned Caesarean Delivery: A Double-Blind Randomised Controlled Trial." BJOG, 2025;132(12):1742-1752. PMID: 40772429.
- [pubmed] Boie S, et al. "Continued versus discontinued oxytocin stimulation in the active phase of labour (CONDISOX): double blind randomised controlled trial." BMJ, 2021;373:n716. PMID: 33853878.
- [pubmed] Bor P, et al. "Continuation versus discontinuation of oxytocin infusion during the active phase of labour: a randomised controlled trial." BJOG, 2016;123(1):129-35. PMID: 26309128.
- [pubmed] Aboshama RA, et al. "High dose vs. low dose oxytocin for labor augmentation: a systematic review and meta-analysis of randomized controlled trials." J Perinat Med, 2021;49(2):178-190. PMID: 32950965.
- [pubmed] Wei RM, et al. "High- vs low-dose oxytocin in lean and obese women: a double-blinded randomized controlled trial." Am J Obstet Gynecol MFM, 2022;4(4):100627. PMID: 35358738.
- [pubmed] Sikich L, et al. "Intranasal Oxytocin in Children and Adolescents with Autism Spectrum Disorder." N Engl J Med, 2021;385(16):1462-1473. PMID: 34644471.
- [pubmed] Hollander E, et al. "Intranasal oxytocin versus placebo for hyperphagia and repetitive behaviors in children with Prader-Willi Syndrome: A randomized controlled pilot trial." J Psychiatr Res, 2021;137:643-651. PMID: 33190843.
- [pubmed] Moerkerke M, et al. "Impact of chronic intranasal oxytocin administration on face expression processing in autistic children: a randomized controlled trial using fMRI." Mol Autism, 2024;15(1):53. PMID: 39709442.
Sources & Citations
Studies were read from their PubMed records (October 5, 2026); the label and Drugs@FDA are listed below with their read dates.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.