Peptides & growth hormone

Oxytocin

Updated · 21 sources · Editorial policy

Oxytocin is a nine-amino-acid peptide hormone produced in the hypothalamus and found in the pituitary gland. It is best known for its roles in childbirth and breastfeeding. Synthetic oxytocin, sold in the US as Pitocin and as generics, is a hospital drug used to induce or strengthen labor and to control bleeding after birth.

Outside obstetrics, oxytocin has been studied, mostly as a nasal spray, for social behavior, sexual function, appetite and muscle. The most important fact for those uses: the only FDA-approved oxytocin nasal spray (Syntocinon) is discontinued, and the large, well-controlled trials of intranasal oxytocin for autism, obesity and trust have found no meaningful effect.

This page summarizes what the FDA label, clinical trials and regulators report. It is for education only and is not medical advice.

Property Detail
Drug class Peptide hormone (nonapeptide); uterotonic (drug that contracts the uterus)
Brands / approval Pitocin (Par), NDA 018261; generic oxytocin injections. Syntocinon nasal spray (NDA 012285) is discontinued
Route (label) Intravenous infusion or intramuscular injection
Strength 10 units/mL
Labeled dose Labor: start 0.5–1 mU/min IV, raised by 1–2 mU/min every 30–60 min. After birth: 10 units IM, or 10–40 units added to an IV infusion
Half-life (label) About 1–6 minutes in plasma
Key mechanism Binds oxytocin receptors in uterine muscle and raises intracellular calcium; receptor numbers peak in early labor at term
US status Prescription only; labor use only in hospital, under supervision
WADA status Not named on the 2026 Prohibited List

What it is

Oxytocin is a nonapeptide, a chain of nine amino acids, part of which is closed into a ring by a sulfur–sulfur (disulfide) bond. The Pitocin label gives the formula C₄₃H₆₆N₁₂O₁₂S₂ and a molecular weight of 1007.19 (FDA label; PubChem). It is a close relative of vasopressin (antidiuretic hormone), differing at only two amino acid positions. That similarity explains why high doses of oxytocin also raise blood pressure and make the kidneys hold water.

Vincent du Vigneaud received the 1955 Nobel Prize in Chemistry in part “for the first synthesis of a polypeptide hormone,” which was oxytocin (Nobel Prize). Modern Pitocin is fully synthetic. The label notes this avoids contamination with vasopressin and other peptides found in pituitary extracts.

Strength is given in units of biological activity rather than milligrams. One 1 mL vial contains 10 units.

Pharmacokinetics

The label lists only intravenous and intramuscular use and describes oxytocin as very short-acting (FDA label):

Parameter Intravenous Intramuscular
Plasma half-life About 1–6 min (shorter in late pregnancy and during lactation) About 1–6 min
Onset of uterine response Almost immediate 3–5 min
Duration of uterine response Subsides within 1 h 2–3 h
Clearance Mainly kidney and liver; little excreted unchanged Same

Because of this short half-life, labor induction uses a continuous pump infusion that can be stopped at once if contractions become too strong.

Intranasal oxytocin

Research trials outside obstetrics have mostly used nasal sprays, typically at 18–40 IU per dose (MacDonald et al., Psychoneuroendocrinology 2011). In 11 volunteers given 24 IU intranasally, plasma oxytocin peaked at 15 minutes, while levels in cerebrospinal fluid (CSF, the fluid around the brain) took up to 75 minutes to rise significantly. Plasma and CSF levels did not correlate (Striepens et al., Sci Rep 2013).

A critical review concluded that very little of a nasal dose appears to reach the CSF, while blood levels rise well above normal, with likely effects on the gut, heart and reproductive tract (Leng and Ludwig, Biol Psychiatry 2016). The authors also noted that many published oxytocin measurements used discredited assay methods.

Approved medical use

The Pitocin label covers two settings (FDA label):

  • Before delivery (antepartum): induction of labor when there is a medical reason, such as preeclampsia near term, maternal diabetes, Rh problems or ruptured membranes; stimulation of labor in selected cases of weak contractions; and as an add-on in incomplete or inevitable abortion.
  • After delivery (postpartum): producing uterine contractions in the third stage of labor and controlling postpartum bleeding.

The label’s boxed notice states that Pitocin is not indicated for elective induction, meaning induction without a medical reason, because the data are inadequate to judge benefit against risk.

Use Labeled regimen
Induction or stimulation of labor IV infusion only. Start 0.5–1 mU/min; increase by 1–2 mU/min at 30–60 min intervals until an adequate contraction pattern. Rates over 9–10 mU/min are rarely needed at term
Postpartum bleeding (IV) 10–40 units added to a running infusion (maximum 40 units per 1000 mL), rate adjusted to keep the uterus contracted
Postpartum bleeding (IM) 10 units after delivery of the placenta
Incomplete, inevitable or elective abortion 10 units in 500 mL IV after curettage; total no more than 30 units in 12 hours in the midtrimester setting

The label notes that infusion rates up to 6 mU/min produce oxytocin levels similar to those of spontaneous labor.

A nasal spray, Syntocinon (40 USP units/mL), was once approved in the US and used by nursing mothers to help empty the breasts (Seifer et al., J Reprod Med 1985). It is now listed as discontinued (Drugs@FDA, NDA 012285).

What the research shows

Preventing postpartum hemorrhage

Postpartum hemorrhage (heavy bleeding after birth) is the leading cause of maternal death worldwide, and the current WHO recommendation for preventing it is 10 IU of oxytocin intramuscularly or intravenously (Gallos et al., Cochrane 2025).

That 2025 Cochrane network meta-analysis pooled 122 randomized trials with 121,931 women. All agents with enough data, including oxytocin, reduced blood loss of at least 500 mL compared with placebo or no treatment. Compared with oxytocin alone:

Agent vs oxytocin Blood loss ≥ 500 mL, risk ratio (95% CI) Certainty
Ergometrine + oxytocin 0.76 (0.64–0.90) High
Misoprostol + oxytocin 0.70 (0.57–0.87) Moderate
Carbetocin Similar to oxytocin High

Oxytocin requires cold storage, which is not available in many countries. The WHO CHAMPION trial randomized 29,645 women in 10 countries to 10 IU oxytocin or 100 μg heat-stable carbetocin by IM injection after vaginal birth (Widmer et al., NEJM 2018):

Outcome Carbetocin Oxytocin Risk ratio (95% CI)
Blood loss ≥ 500 mL or extra uterotonic 14.5% 14.4% 1.01 (0.95–1.06)
Blood loss ≥ 1000 mL 1.51% 1.45% 1.04 (0.87–1.25)

Carbetocin was noninferior for the first outcome. Noninferiority could not be shown for severe bleeding because events were rare.

Sexual function and libido

Oxytocin is released during sex. In 9 men and 13 women, plasma oxytocin rose during sexual arousal and was significantly higher during orgasm than at baseline (Carmichael et al., JCEM 1987). Whether giving extra oxytocin improves sexual function is much less clear:

  • Healthy couples. In 29 couples (58 people) given 24 IU intranasally, oxytocin did not change sexual drive, arousal, erection or lubrication. It increased ratings of orgasm intensity and contentment after sex, with small to moderate effect sizes (Behnia et al., Horm Behav 2014).
  • Women with sexual dysfunction. In a 22-week double-blind crossover trial in 30 pre- and postmenopausal women, 32 IU of intranasal oxytocin before intercourse was compared with placebo over 8 weeks each. Sexual function scores rose by 26% on oxytocin and 31% on placebo, with no significant difference between treatments (Muin et al., Fertil Steril 2015).

No oxytocin product is approved for low libido or erectile dysfunction. For a peptide developed specifically for low sexual desire, see PT-141 (bremelanotide).

Muscle and body composition

The muscle interest comes mainly from animal work. In mice, oxytocin was needed for normal muscle regeneration, blood levels fell with age, and mice lacking oxytocin developed early muscle loss (Elabd et al., Nat Commun 2014). These are mouse results and have not been shown to apply to people.

Human data are limited to small or negative trials:

Trial Population, n Regimen Main result
Espinoza et al., JAMDA 2021 (pilot) Older adults with obesity and slow gait, 21 24 IU intranasal 4×/day, 8 weeks Lean mass +2.25 kg vs placebo; LDL −19.3 mg/dL; no change in BMI
Plessow et al., NEJM Evid 2024 Adults with obesity, 61 24 IU intranasal 4×/day, 8 weeks No difference in weight (+0.20 vs +0.26 kg); no benefit on fat mass, visceral fat, liver fat or energy expenditure

The pilot was small and described itself as proof of concept. The larger trial, using the same regimen, found no effect on body weight or body composition. We found no controlled trial testing whether oxytocin builds muscle in healthy or trained adults.

Social behavior, trust and autism

A widely cited 2005 study reported that intranasal oxytocin increased trust in an economic game (Kosfeld et al., Nature 2005). Larger replications have not confirmed it. A 2026 registered replication in 211 people found no effect, and pooling it with an earlier replication (532 people in total) placed any effect within a negligibly small range (Kroll et al., Cortex 2026).

A statistical review of the field concluded that intranasal oxytocin studies are generally underpowered and that most published findings are probably not true effects (Walum et al., Biol Psychiatry 2016).

The largest clinical test was a 24-week phase 2 trial in 290 children and adolescents with autism, using a target dose of 48 IU daily (Sikich et al., NEJM 2021). The social withdrawal score improved by 3.7 points on oxytocin and 3.5 on placebo (difference −0.2; 95% CI −1.5 to 1.0; P = 0.61). Secondary social and cognitive outcomes also did not differ.

Side effects and risks

The label’s main warnings concern use during labor (FDA label):

  • Uterine overstimulation. Excessive dosing or hypersensitivity can cause hypertonic or tetanic contractions and uterine rupture.
  • Fetal effects. Reported effects include slow heart rate, arrhythmias, low Apgar scores, neonatal jaundice, retinal hemorrhage, permanent brain damage, seizures and fetal death.
  • Maternal events. Reported events include anaphylaxis, arrhythmias, hypertensive episodes, subarachnoid hemorrhage, postpartum hemorrhage, fatal afibrinogenemia (loss of a clotting protein), nausea and vomiting. Maternal deaths have been reported.

The label requires continuous observation by trained staff and electronic monitoring of contractions and fetal heart rate.

Water intoxication

Because oxytocin acts like vasopressin at high doses, it makes the kidneys retain water. This can dilute blood sodium (hyponatremia). The label reports severe water intoxication with convulsions and coma, including maternal death, and links it especially to large doses (40–50 mU/min) infused for long periods.

The same risk has been reported with nasal spray misuse. A case report described a nursing mother who developed severe water intoxication, hyponatremic encephalopathy (brain dysfunction from low sodium) and convulsions after excessive, unmonitored use of an oxytocin nasal spray while receiving IV fluids (Seifer et al., J Reprod Med 1985).

Intranasal use in research

A systematic review of 38 randomized trials (1,529 participants, 79% male) found that short-term doses of 18–40 IU caused no more side effects than placebo, and participants could not tell which they had received (MacDonald et al., Psychoneuroendocrinology 2011). The authors noted that long-term, higher-dose use and use in women and vulnerable groups had not been well studied. In the 24-week autism trial, adverse events were similar on oxytocin and placebo.

Interactions and contraindications

The label lists these interactions:

  • severe hypertension when oxytocin was given 3–4 hours after a vasoconstrictor used with caudal block anesthesia;
  • hypotension, sinus bradycardia and abnormal heart rhythms with cyclopropane anesthesia.

Antepartum use is contraindicated in cephalopelvic disproportion (the baby cannot fit through the pelvis), unfavorable fetal positions, obstetric emergencies favoring surgery, fetal distress when delivery is not imminent, a uterus that is already hyperactive, conditions in which vaginal delivery is contraindicated, and hypersensitivity to the drug.

Oxytocin injection is a prescription drug in the US, and the label restricts its use for labor to the hospital. The only US-approved nasal spray is discontinued, so nasal oxytocin products sold for libido or bonding are not FDA-approved drugs.

Oxytocin is not named on the WADA 2026 Prohibited List. The list’s peptide hormone section (S2) names other hormones, such as chorionic gonadotrophin, GnRH analogs and kisspeptin, but not oxytocin.

Key takeaways

  • An obstetric drug first. Approved oxytocin is an IV or IM hospital drug for medically indicated labor induction and postpartum bleeding, not for elective induction.
  • Extremely short-acting. The plasma half-life is about 1–6 minutes, which is why labor dosing uses a continuous infusion that can be stopped at once.
  • Central to preventing postpartum hemorrhage. It is the WHO standard, and a 122-trial Cochrane analysis found combining it with ergometrine or misoprostol reduced bleeding further.
  • Water intoxication is the key non-obvious risk. Its vasopressin-like effect can drop blood sodium. The label reports seizures, coma and deaths with infusions, and seizures have been reported with nasal spray misuse.
  • Nasal spray claims outrun the evidence. Large controlled trials found no benefit for autism, obesity or trust, and a trial in women with sexual dysfunction found no difference from placebo.
  • Muscle data are mostly from mice. One 21-person pilot reported more lean mass in older adults with obesity, but a larger obesity trial found no body-composition benefit.

Sources

  1. Par Health USA. Pitocin (oxytocin injection, USP) synthetic, prescribing information, revised March 2026. DailyMed; Drugs@FDA, NDA 018261.
  2. Food and Drug Administration. Syntocinon (oxytocin) nasal solution, 40 USP units/mL, NDA 012285: marketing status discontinued. Drugs@FDA.
  3. National Center for Biotechnology Information. Oxytocin, PubChem CID 439302. PubChem.
  4. Nobel Prize Outreach. The Nobel Prize in Chemistry 1955: Vincent du Vigneaud. Nobel Prize.
  5. Striepens N, Kendrick KM, Hanking V, et al. Elevated cerebrospinal fluid and blood concentrations of oxytocin following its intranasal administration in humans. Sci Rep. 2013;3:3440. PubMed.
  6. Leng G, Ludwig M. Intranasal oxytocin: myths and delusions. Biol Psychiatry. 2016;79(3):243–250. PubMed.
  7. Gallos ID, Yunas I, Devall AJ, et al. Uterotonic agents for preventing postpartum haemorrhage: a network meta-analysis. Cochrane Database Syst Rev. 2025;4(4):CD011689. PubMed.
  8. Widmer M, Piaggio G, Nguyen TMH, et al. Heat-stable carbetocin versus oxytocin to prevent hemorrhage after vaginal birth. N Engl J Med. 2018;379(8):743–752. PubMed.
  9. Carmichael MS, Humbert R, Dixen J, Palmisano G, Greenleaf W, Davidson JM. Plasma oxytocin increases in the human sexual response. J Clin Endocrinol Metab. 1987;64(1):27–31. PubMed.
  10. Behnia B, Heinrichs M, Bergmann W, et al. Differential effects of intranasal oxytocin on sexual experiences and partner interactions in couples. Horm Behav. 2014;65(3):308–318. PubMed.
  11. Muin DA, Wolzt M, Marculescu R, et al. Effect of long-term intranasal oxytocin on sexual dysfunction in premenopausal and postmenopausal women: a randomized trial. Fertil Steril. 2015;104(3):715–723.e4. PubMed.
  12. Elabd C, Cousin W, Upadhyayula P, et al. Oxytocin is an age-specific circulating hormone that is necessary for muscle maintenance and regeneration. Nat Commun. 2014;5:4082. PubMed.
  13. Espinoza SE, Lee JL, Wang CP, et al. Intranasal oxytocin improves lean muscle mass and lowers LDL cholesterol in older adults with sarcopenic obesity: a pilot randomized controlled trial. J Am Med Dir Assoc. 2021;22(9):1877–1882.e2. PubMed.
  14. Plessow F, Kerem L, Wronski ML, et al. Intranasal oxytocin for obesity. NEJM Evid. 2024;3(5):EVIDoa2300349. PubMed.
  15. Kosfeld M, Heinrichs M, Zak PJ, Fischbacher U, Fehr E. Oxytocin increases trust in humans. Nature. 2005;435(7042):673–676. PubMed.
  16. Kroll CF, Schruers KRJ, Viechtbauer W, et al. Absence of a meaningful effect of intranasal oxytocin on trusting behavior: a registered report with pooled equivalence testing. Cortex. 2026;198:208–233. PubMed.
  17. Walum H, Waldman ID, Young LJ. Statistical and methodological considerations for the interpretation of intranasal oxytocin studies. Biol Psychiatry. 2016;79(3):251–257. PubMed.
  18. Sikich L, Kolevzon A, King BH, et al. Intranasal oxytocin in children and adolescents with autism spectrum disorder. N Engl J Med. 2021;385(16):1462–1473. PubMed.
  19. Seifer DB, Sandberg EC, Ueland K, Sladen RN. Water intoxication and hyponatremic encephalopathy from the use of an oxytocin nasal spray: a case report. J Reprod Med. 1985;30(3):225–228. PubMed.
  20. MacDonald E, Dadds MR, Brennan JL, Williams K, Levy F, Cauchi AJ. A review of safety, side-effects and subjective reactions to intranasal oxytocin in human research. Psychoneuroendocrinology. 2011;36(8):1114–1126. PubMed.
  21. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026. WADA 2026 Prohibited List.