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This is an approved / prescription medicine. Do not use without a prescription and medical supervision.

EMA-approvedaka Tractocile, Antocin

Atosiban — Complete Research Guide (2026)

Last updated 2026-06-30

TL;DR

Atosiban (also known as Tractocile) is a peptide catalogued under Sexual Health (Oxytocin/vasopressin V1a antagonist). It is described as: Oxytocin receptor antagonist. Documented context: Preterm labor. Neutral reference entry; EU status: EU-approved prescription medicine.

What is Atosiban?

Atosiban is a peptide oxytocin/vasopressin V1a receptor antagonist used as a tocolytic to delay imminent preterm birth. It is approved in the European Union (Tractocile) to postpone imminent preterm delivery in pregnant adults with regular uterine contractions between 24 and 33 weeks of gestation; it is NOT FDA-approved and is not marketed in the United States.

Its evidence base is human randomized controlled trials comparing it mainly with beta-agonist tocolytics and, more recently, with nifedipine and placebo, plus Cochrane systematic reviews.

It is a hospital obstetric medicine, not a consumer product.

How does Atosiban work?

Atosiban competitively blocks oxytocin receptors (and related vasopressin V1a receptors) on uterine myometrium, reducing oxytocin-driven intracellular calcium release.

This dampens the frequency and force of uterine contractions.

What does the research say about Atosiban?

  • Atosiban delayed preterm delivery with clinical effectiveness comparable to beta-agonists but with markedly fewer maternal cardiovascular side effects in the Worldwide Atosiban versus Beta-agonists randomized trials. [1]
  • Compared directly with ritodrine, atosiban achieved similar tocolytic effectiveness while being better tolerated in a multicentre double-blind randomized trial. [2]
  • Versus oral nifedipine, 48 hours of atosiban tocolysis produced similar perinatal outcomes in the randomized APOSTEL III trial. [4]

Clinical research & studies

The references below are the primary sources cited throughout this guide. Each links directly to PubMed or the regulator. Where evidence is preclinical (animal or in-vitro), that is stated rather than implied.

  • [1] Effectiveness and safety of the oxytocin antagonist atosiban versus beta-adrenergic agonists in the treatment of preterm labour — Worldwide Atosiban versus Beta-agonists Study Group, BJOG 2001. (Pooled multinational randomized controlled trials)
  • [2] Double-blind, randomized, controlled trial of atosiban and ritodrine in the treatment of preterm labor: a multicenter effectiveness and safety study — Moutquin JM et al., American Journal of Obstetrics and Gynecology 2000. (Randomized controlled trial)
  • [3] An oxytocin receptor antagonist (atosiban) in the treatment of preterm labor: a randomized, double-blind, placebo-controlled trial with tocolytic rescue — Romero R et al., American Journal of Obstetrics and Gynecology 2000. (Randomized, double-blind, placebo-controlled trial)
  • [4] Nifedipine versus atosiban for threatened preterm birth (APOSTEL III): a multicentre, randomised controlled trial — van Vliet EOG et al., Lancet 2016. (Randomized controlled trial (APOSTEL III))
  • [5] Oxytocin receptor antagonists for inhibiting preterm labour — Flenady V et al., Cochrane Database of Systematic Reviews 2014. (Cochrane systematic review)

Dosing context

This is not medical advice or a usage recommendation. Dosing figures are reported research context only, cited from the published literature.

Atosiban is given intravenously in hospital as an initial bolus followed by a loading infusion and then a maintenance infusion, typically for up to 48 hours, to buy time for corticosteroids and, if needed, transfer to a unit with neonatal intensive care.

This is context only: dosing, gestational-age eligibility and duration are determined by obstetric teams with maternal and fetal monitoring, and it is not self-administered.

Side effects & safety profile

Atosiban is generally well tolerated, with far fewer maternal cardiovascular effects than beta-agonists; the most common effects are injection-site reactions, nausea, headache and dizziness.

Unlike the vasoconstrictor vasopressin analogues, it is a receptor antagonist and is not associated with maternal ischaemia.

Its clinical value is debated: a Cochrane review found atosiban did not clearly reduce birth within 48 hours or improve neonatal outcomes versus placebo or other agents, and one placebo-controlled trial raised a signal of more extremely preterm births and infant deaths in a subgroup, so it is used for short-term delay under obstetric supervision rather than as a proven improver of newborn outcomes.

Stacking & combinations

In obstetric practice tocolysis with atosiban is timed alongside antenatal corticosteroids (and sometimes magnesium sulfate for neuroprotection) under specialist supervision, not combined with unregulated peptides.

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Frequently asked questions

No. Atosiban is approved in the European Union and many other countries as a tocolytic (brand Tractocile) but is not FDA-approved or marketed in the United States.

References

  1. [1] Effectiveness and safety of the oxytocin antagonist atosiban versus beta-adrenergic agonists in the treatment of preterm labour — Worldwide Atosiban versus Beta-agonists Study Group, BJOG 2001. PMID: 11236112. View sourceStudy: Pooled multinational randomized controlled trialsAtosiban matched beta-agonists for tocolytic effectiveness while causing substantially fewer maternal cardiovascular adverse events.
  2. [2] Double-blind, randomized, controlled trial of atosiban and ritodrine in the treatment of preterm labor: a multicenter effectiveness and safety study — Moutquin JM et al., American Journal of Obstetrics and Gynecology 2000. PMID: 10819857. View sourceStudy: Randomized controlled trialAtosiban was comparable in effectiveness to ritodrine but better tolerated, with fewer significant maternal or fetal adverse events.
  3. [3] An oxytocin receptor antagonist (atosiban) in the treatment of preterm labor: a randomized, double-blind, placebo-controlled trial with tocolytic rescue — Romero R et al., American Journal of Obstetrics and Gynecology 2000. PMID: 10819855. View sourceStudy: Randomized, double-blind, placebo-controlled trialAtosiban prolonged pregnancy up to 7 days at gestational age 28 weeks or more with low rates of maternal-fetal adverse effects.
  4. [4] Nifedipine versus atosiban for threatened preterm birth (APOSTEL III): a multicentre, randomised controlled trial — van Vliet EOG et al., Lancet 2016. PMID: 26944026. View sourceStudy: Randomized controlled trial (APOSTEL III)48 hours of tocolysis with atosiban or nifedipine produced similar perinatal outcomes in threatened preterm birth.
  5. [5] Oxytocin receptor antagonists for inhibiting preterm labour — Flenady V et al., Cochrane Database of Systematic Reviews 2014. PMID: 24903678. View sourceStudy: Cochrane systematic reviewAtosiban caused fewer maternal side effects than betamimetics but did not clearly prevent preterm birth or improve neonatal outcomes.
This article is for educational and research purposes only. Peptides discussed here are not approved for human consumption by the FDA, EMA, or equivalent regulators outside of specific clinical contexts. Always consult a licensed medical professional before any therapeutic use.