Parturition, lactation, and social bonding from a 9-residue peptide. Structurally it is Cyclic nonapeptide (9 aa).

How strong is the evidence for Oxytocin?

PeptideHormone grades Oxytocin at the "Established" evidence tier — its mechanism and core effects are settled across the peer-reviewed literature. It is catalogued as an endogenous signal the body produces itself, and the tier is an editorial judgment about the public literature that can change as the science does.

What is the half-life of Oxytocin?

The reported circulating half-life of Oxytocin is ~1–6 min.

Oxytocin

Parturition, lactation, and social bonding from a 9-residue peptide.

EndogenousEstablished

Nine residues running parturition, milk, and attachment. The disproportion between the size of the molecule and the size of the job is the whole field in miniature.

Identity

Class: Cyclic nonapeptide (9 aa)
Source: Hypothalamus (PVN/SON); released from the posterior pituitary
Receptor: Oxytocin receptor (OXTR), a class A GPCR

Key properties

Evidence floorClinicalREF1CLIN1

Molecular weight

~1,007.2 Da

REF

Half-life (native)

~1–6 min

CLIN

Model dosing

Approximate values for the native hormone; engineered analogs are often deliberately larger and far longer-acting. Each figure carries its own provenance tier, and the floor is the weakest of them - the Standard.

Mechanism

Synthesized in the hypothalamus and released from the posterior pituitary, oxytocin drives uterine contraction in labor and milk ejection in lactation, and acts centrally in social and affiliative behavior. It differs from vasopressin by only two amino acids.

Reference notes

Oxytocin and vasopressin differ by just two residues yet act on distinct receptor families.
Its central (behavioral) and peripheral (reproductive) roles reflect receptor distribution, not different ligands.
It is a textbook example of how small sequence differences encode large functional ones.

Common questions

What is Oxytocin?: Parturition, lactation, and social bonding from a 9-residue peptide. Structurally it is Cyclic nonapeptide (9 aa).
How does Oxytocin work?: Synthesized in the hypothalamus and released from the posterior pituitary, oxytocin drives uterine contraction in labor and milk ejection in lactation, and acts centrally in social and affiliative behavior. It differs from vasopressin by only two amino acids.
How strong is the evidence for Oxytocin?: PeptideHormone grades Oxytocin at the "Established" evidence tier — its mechanism and core effects are settled across the peer-reviewed literature. It is catalogued as an endogenous signal the body produces itself, and the tier is an editorial judgment about the public literature that can change as the science does.
What is the half-life of Oxytocin?: The reported circulating half-life of Oxytocin is ~1–6 min.

Selected literature

Curated peer-reviewed reviews, sourced from PubMed. Selected for relevance, not exhaustive — open any entry on PubMed for the full record and its primary citations.

1.The physiology and pharmacology of oxytocin in labor and in the peripartum period · American journal of obstetrics and gynecology, 2024 · PMID 38462255
2.Oxytocin, Neural Plasticity, and Social Behavior · Annual review of neuroscience, 2021 · PMID 33823654

External references

Oxytocin in the public knowledge graph — the same entity resolved across the authoritative chemistry and protein databases.