Peptide Basics
Peptide Hormones: What They Are, Examples and How They Differ From Steroid Hormones
Peptide hormones are hormones built from amino acids joined by peptide bonds, released into the blood to act on distant organs. They range from three amino acids (TRH) to protein-sized chains such as growth hormone (191), and include insulin, glucagon, oxytocin and GLP-1. This page sets out the definition the U.S. National Library of Medicine uses, fourteen hormones with their exact lengths checked in UniProt, how the body cuts them from longer precursors, how they differ from steroid and amine hormones, and how peptide medicines copy or modify them.
What makes a peptide a hormone
MeSH defines a hormone as a substance with a specific regulatory effect on the activity of an organ, originally one secreted by an endocrine gland and carried in the blood to its target. A peptide hormone is such a hormone made from amino acids. The distinction MeSH draws is distance: a peptide hormone acts systemically, across the body, while intercellular signalling peptides act locally, on a neighbouring cell. The same chemistry, a short chain of amino acids (see what peptides are), can do either job.
MeSH files 28 groups under peptide hormones, among them the hypothalamic, pituitary, pancreatic and placental hormones, the natriuretic peptides that regulate water and salt balance, the angiotensins of blood-pressure control, gastrin, secretin, ghrelin, calcitonin, parathyroid hormone and thymosin. Size is not the test: pituitary hormones, MeSH notes, include small peptides, proteins and glycoproteins, and the major gonadotropins are glycoproteins.
Peptide hormone examples, shortest to longest
Every length below is the human sequence as UniProt records it; the group is the MeSH heading the hormone sits under.
| Hormone | MeSH group | Amino acids | Note |
|---|---|---|---|
| Thyrotropin-releasing hormone (TRH) | Pituitary hormone-releasing hormones | 3 | Six copies sit in one 218-residue precursor; each ends in a proline amide. |
| Oxytocin | Posterior pituitary hormones | 9 | A ring closed by a disulfide bond; cut from a precursor that also yields neurophysin 1. |
| Vasopressin | Posterior pituitary hormones; neuropeptides | 9 | Its precursor also releases neurophysin 2 and a 39-residue fragment, copeptin. |
| Gonadotropin-releasing hormone (GnRH) | Pituitary hormone-releasing hormones | 10 | Starts with pyroglutamate and ends in glycine amide. |
| Somatostatin | Pancreatic hormones; pituitary hormone release-inhibiting hormones | 14 or 28 | Two lengths are cut from one precursor; in the pancreas the delta cells secrete it. |
| Ghrelin | Peptide hormones (own heading) | 28 | Carries a fatty acyl group; made mainly in the stomach in adults. |
| Glucagon | Pancreatic hormones | 29 | Made by pancreatic alpha cells, from proglucagon. |
| GLP-1 (7-36) amide | Glucagon-like peptides | 30 | Same precursor as glucagon, cut at a different place. |
| Calcitonin | Peptide hormones; neuropeptides; thyroid hormones | 32 | Ends in a proline amide. |
| Corticotropin (ACTH) | Melanocortins | 39 | One of several hormones cut from the precursor POMC. |
| Growth hormone-releasing hormone (GHRH) | Pituitary hormone-releasing hormones | 44 | Ends in a leucine amide. |
| Insulin | Pancreatic hormones | 51 (21 + 30) | Two chains, A and B, from pancreatic beta cells. |
| Parathyroid hormone (PTH) | Peptide hormones (own heading) | 84 | One chain. |
| Growth hormone (somatotropin) | Anterior pituitary hormones | 191 | A protein-sized hormone, still filed under peptide hormones. |
Sources: UniProt P20396, P01178, P01185, P01148, P61278, P01275, Q9UBU3, P01308, P01258, P01189, P01286, P01270 and P01241; NLM MeSH descriptors D036361, D007028, D010907, D010187, D054439, D013004, D010121, D014667, D013973, D007987, D013007, D052216, D000324, D013006, D002116 and D010281. Read 28 October 2026.
How the body makes them: one precursor, several hormones
Peptide hormones are made from a gene, but rarely in their final form. The cell builds a longer precursor protein and cuts the hormone out of it. UniProt’s records show how much one precursor can hold:
- Proglucagon yields glucagon (29), GLP-1 (30 in its 7-36 amide form), GLP-2 (33) and oxyntomodulin (37).
- POMC yields corticotropin (ACTH, 39), alpha-MSH (13) and beta-endorphin (31).
- The TRH precursor, 218 amino acids long, contains six copies of the three-amino-acid hormone.
- The vasopressin precursor also releases a carrier protein, neurophysin 2, and a 39-residue fragment called copeptin.
- Insulin starts as one chain, proinsulin, and is cut into its A and B chains.
Many are finished with an amide at the end of the chain, which UniProt records as a modified residue: glycine amide on oxytocin, vasopressin and GnRH, proline amide on TRH and calcitonin, leucine amide on GHRH. Ghrelin also carries a fatty acyl group.
Sources: UniProt P01275, P01189, P20396, P01185, P01308, P01178, P01148, P01258, P01286 and Q9UBU3; MeSH D054439. Read 28 October 2026.
Peptide vs steroid vs amine hormones
Hormones are commonly grouped into three chemical families, and the families differ in where their receptors sit: a peptide chain is received at the cell surface, while a steroid’s receptor usually sits inside the cell.
| Family | Built from | Examples | Where the receptor is |
|---|---|---|---|
| Peptide hormones | Chains of amino acids | Insulin, glucagon, oxytocin, growth hormone | Receptors on the cell surface bind them and relay the signal inside. |
| Steroid hormones | A fused 17-carbon ring system, the family that includes cholesterol | Estradiol, progesterone, testosterone | Receptors usually sit in the cytoplasm or nucleus; the hormone-receptor complex regulates genes. |
| Amino-acid-derived (amine) hormones | Derived from amino acids, not built as a chain | Thyroxine (thyroid); adrenaline and noradrenaline, catecholamines made from tyrosine | Differs by hormone; no single rule covers the group. |
Sources: NLM MeSH descriptors Receptors, Peptide (D018000), Steroids (D013256), Gonadal Steroid Hormones (D012739), Receptors, Steroid (D011987), Thyroid Hormones (D013963) and Catecholamines (D002395). Read 28 October 2026.
Peptide hormones as medicines: copies and analogues
Several approved medicines are peptide hormones or are built on one. Their U.S. labels show the two approaches: copy the natural sequence, or change it so the molecule survives longer in the body.
| Medicine | Hormone it is based on | What the label says |
|---|---|---|
| Insulin human (Humulin R) | Insulin | The human sequence, made by recombinant DNA in E. coli. |
| Oxytocin (Pitocin) | Oxytocin | Synthetic oxytocin; the label calls it a nonapeptide. |
| Teriparatide | Parathyroid hormone | Identical to the first 34 of the hormone’s 84 amino acids; recombinant. |
| Leuprolide | GnRH | A synthetic nonapeptide analog of the natural 10-amino-acid hormone. |
| Octreotide (Sandostatin) | Somatostatin | A cyclic octapeptide (8) that mimics the hormone’s actions. |
| Semaglutide (Ozempic) | GLP-1 | A GLP-1 receptor agonist: position 8 changed to resist the enzyme DPP-4, and a fatty di-acid added so it binds albumin. |
Larger hormones such as insulin and growth hormone, with more than 40 amino acids, have been regulated in the United States as biologics since March 2020; the peptide vs protein page explains that line.
Sources: U.S. labels via openFDA for Humulin R (effective 31 October 2023), Pitocin (6 May 2026), teriparatide injection (27 May 2025), Vabrinty leuprolide acetate (30 April 2026), Sandostatin (22 July 2026) and Ozempic/Rybelsus (30 January 2026). Read 28 October 2026.
Where research compounds fit
Many research peptides are natural hormones or fragments and analogues of them. Gonadorelin has the same ten-amino-acid sequence as GnRH; sermorelin is the first 29 amino acids of the 44 in GHRH; tesamorelin is a modified analogue of the full GHRH chain; kisspeptin-10 is the last ten amino acids of the 54-residue kisspeptin; oxytocin and VIP are the hormones themselves; thymosin alpha-1 belongs to the thymosin family MeSH files under peptide hormones; and semaglutide is a GLP-1 analogue. Each guide sets out the compound’s identity, research history and regulatory status.
Medibact does not manufacture or sell peptides. We supply USP-grade bacteriostatic water, made in the USA, for research use only, and publish reference material like this page.
Where this sits in the rest of the reference
FAQ
What are peptide hormones?
Peptide hormones are hormones built from amino acids joined by peptide bonds. The U.S. National Library of Medicine’s MeSH vocabulary defines them as hormones synthesized from amino acids whose actions are systemic, which separates them from signalling peptides that act only on nearby cells. They range from thyrotropin-releasing hormone, three amino acids long, to protein-sized hormones such as growth hormone, with 191.
What are examples of peptide hormones?
Insulin and glucagon from the pancreas; oxytocin and vasopressin, released from the posterior pituitary; growth hormone from the anterior pituitary; corticotropin (ACTH), cut from the precursor POMC; the hypothalamic releasing hormones TRH, GnRH and GHRH; somatostatin; ghrelin from the stomach; GLP-1; calcitonin; and parathyroid hormone. MeSH lists 28 groups under peptide hormones, including the natriuretic peptides, angiotensins, gastrin, secretin and thymosin.
What is the difference between peptide and steroid hormones?
They are built differently and are received differently. Peptide hormones are chains of amino acids, and they are bound by receptors on the cell surface. Steroid hormones such as estradiol, progesterone and testosterone share a fused 17-carbon ring system, the chemical family of cholesterol, and their receptors usually sit inside the cell, in the cytoplasm or nucleus, where the hormone-receptor complex regulates genes.
Is insulin a peptide hormone?
Yes. Insulin is a peptide hormone of 51 amino acids in two chains, an A chain of 21 and a B chain of 30, secreted by the beta cells of the pancreas. It is made first as a longer single chain, proinsulin, which is then cut.
Is glucagon a peptide hormone?
Yes. Glucagon is a 29-amino-acid peptide hormone secreted by the alpha cells of the pancreas. It is cut from a precursor, proglucagon, which also yields GLP-1, GLP-2 and oxyntomodulin.
Is growth hormone a peptide hormone?
Yes, although at 191 amino acids it is large enough to be a protein. MeSH files pituitary hormones as small peptides, proteins and glycoproteins under the peptide hormone heading, and the U.S. FDA has regulated growth hormone as a biologic since March 2020 because it has more than 40 amino acids.
How are peptide hormones made in the body?
From a gene, as part of a longer precursor that is cut into the active hormone. One precursor can yield several hormones: POMC gives corticotropin, alpha-MSH and beta-endorphin, and proglucagon gives glucagon and GLP-1. Many hormones are finished with an amide at their end, as UniProt records for oxytocin, GnRH, GHRH and calcitonin.
Are peptide medicines the same as the natural hormones?
Some are identical copies and some are modified. U.S. labels describe human insulin and oxytocin with the natural sequences, made by recombinant DNA or chemical synthesis; teriparatide is the first 34 amino acids of parathyroid hormone; leuprolide, octreotide and semaglutide are analogues changed to last longer or act more strongly than the hormone they are based on.
Is this medical advice?
No. This page explains what peptide hormones are, from public scientific and regulatory sources. It gives no dose, protocol or recommendation, and peptides sold for research are labelled research use only, not for human use. Medibact supplies USP-grade bacteriostatic water, made in the USA, and is not affiliated with any manufacturer of the products named here.
References: NLM MeSH descriptors D036361, D006728, D036341, D007028, D010907, D010187, D006062, D054439, D013947, D018000, D013256, D012739, D011987, D013963 and D002395; UniProt P20396, P01178, P01185, P01148, P61278, P01275, Q9UBU3, P01308, P01258, P01189, P01286, P01270, P01241, P01282 and Q15726; U.S. labels for Humulin R, Pitocin, teriparatide, Vabrinty, Sandostatin and Ozempic/Rybelsus via openFDA. Read 28 October 2026.
Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.