Peptide Basics
Ghrelin: The Hunger Hormone as a Peptide, Its Receptor and the Drugs That Copy It
Ghrelin is a 28-amino-acid peptide hormone made mainly in the stomach. It increases appetite and makes the pituitary release growth hormone, and it only works with a fatty acid attached to its third amino acid. This page sets out what the ghrelin molecule is, the precursor it shares with obestatin, the enzyme that adds its fatty acid, the receptor it acts on, how it differs from leptin, and where the medicines and research compounds that act on the same receptor stand with regulators. Every figure is taken from UniProt, PubChem, MeSH, PubMed, Drugs@FDA or the World Anti-Doping Agency’s list.
What ghrelin is
Ghrelin is one of the peptide hormones. MeSH describes it as a 28-amino-acid, acylated, orexigenic peptide — orexigenic meaning it stimulates appetite — that binds growth hormone secretagogue receptors, and notes that in adults it is made mainly in the stomach. It was identified in 1999 by Kojima and colleagues, who reported it in Nature as a growth-hormone-releasing acylated peptide from the stomach.
UniProt records three roles for it: it is the ligand of the growth hormone secretagogue receptor, it makes the pituitary release growth hormone, and it stimulates appetite, fat gain and gastric acid secretion. It is found in the blood in all its forms, and when the stomach is removed, other tissues take over part of its production.
The human mature peptide reads GSSFLSPEHQRVQQRKESKKPPAKLQPR. PubChem gives the acylated form a molecular formula of C149H249N47O42 and a molecular weight of 3,370.9 (CID 16133832).
One precursor, two peptides: ghrelin and obestatin
Ghrelin is cut from a precursor of 117 amino acids that MeSH also calls motilin-related peptide. UniProt maps the pieces as follows, by position in the precursor:
| Part | Positions | Amino acids | What it is |
|---|---|---|---|
| Signal peptide | 1-23 | 23 | Steers the chain into the secretory pathway, then is cut off. |
| Ghrelin-28 | 24-51 | 28 | The main form. Its third amino acid, a serine, carries a fatty acid. |
| Ghrelin-27 | 24-50 | 27 | A shorter form, also found in blood. |
| Propeptide | 52-75 | 24 | Removed; no hormone of its own is assigned to it. |
| Obestatin | 76-98 | 23 | A second peptide cut from the same precursor, ending in a leucine amide. |
| Propeptide | 99-117 | 19 | Removed in the mature form. |
Obestatin was described in Science in 2005 as a peptide encoded by the ghrelin gene that opposes ghrelin’s effect on food intake. UniProt lists that appetite-reducing role as inferred by similarity, not as shown directly in humans, and records that the amide at its end is essential for its activity.
Sources: UniProt Q9UBU3; MeSH D054439; PubMed 16284174 (Zhang and colleagues, Science 2005). Read 3 November 2026.
The fatty acid that switches ghrelin on
Ghrelin is unusual among peptide hormones: its third amino acid, a serine, carries a fatty acid. Most often it is an octanoyl group, eight carbons long; hexanoyl (six) and decanoyl (ten) forms also occur, and UniProt notes small amounts of acetyl and butyryl forms. The enzyme that attaches it is ghrelin O-acyltransferase, GOAT, a membrane enzyme of 435 amino acids encoded by the MBOAT4 gene and found mainly in the stomach. It was identified in 2008.
UniProt records that this acylation is essential for ghrelin to activate its receptor. Ghrelin without the fatty acid is called des-acyl ghrelin. Our page on how peptides are made explains how synthetic peptides are made.
Sources: UniProt Q9UBU3 (PTM) and Q96T53 (MBOAT4); PubMed 18443287 (Gutierrez and colleagues, PNAS 2008). Read 3 November 2026.
The ghrelin receptor, GHS-R1a
Ghrelin acts on the growth hormone secretagogue receptor type 1, a G protein-coupled receptor of 366 amino acids that UniProt places in the pituitary and hypothalamus. When ghrelin binds, the receptor signals through Gq proteins; UniProt records that its activation stimulates appetite and promotes growth hormone secretion.
The receptor was known before its hormone. Synthetic growth hormone-releasing peptides (GHRPs) such as GHRP-6 had been made and shown to bind it, so it was named after them; ghrelin was found afterwards as its natural ligand. That is why ghrelin sits at the centre of our growth hormone peptides page, next to GHRH and somatostatin.
Source: UniProt Q92847. Read 3 November 2026.
Ghrelin vs leptin
Ghrelin and leptin are often paired because they push appetite in opposite directions. They are also very different molecules:
| Ghrelin | Leptin | |
|---|---|---|
| Size | 28 amino acids (about 3.4 kDa) | 146 amino acids after its signal is removed |
| Main source | Stomach | Fat (adipose) tissue |
| Receptor | GHS-R1a (growth hormone secretagogue receptor) | LEPR (leptin receptor) |
| Effect on food intake, as UniProt records it | Increases it | Decreases it |
| Other role | Makes the pituitary release growth hormone | Regulates energy balance, acting on the hypothalamus |
| Peptide or protein? | A peptide | Protein-sized, though both are called hormones |
Sources: UniProt Q9UBU3, Q92847 and P41159 (leptin, 167 amino acids including a 21-residue signal); PubChem CID 16133832. Read 3 November 2026.
Medicines and research compounds that act on the ghrelin receptor
Several molecules have been built to switch on the ghrelin receptor. Most of them are not peptides. None is a ghrelin medicine approved in the United States today: a search of Drugs@FDA on 3 November 2026 returned no record for ghrelin, its international nonproprietary name lenomorelin, anamorelin or relamorelin.
| Compound | What it is | Approval record | WADA 2026 |
|---|---|---|---|
| Anamorelin | Small molecule (C31H42N6O3, 546.7) | Approved in Japan on 11 December 2020 for cancer cachexia in four cancers; not approved in Europe; no Drugs@FDA record | Named in S2.2.4 |
| Macimorelin (Macrilen) | Small molecule (C26H30N6O3, 474.6) | FDA-approved in 2017 to diagnose adult growth hormone deficiency; now listed as discontinued | Named in S2.2.4 |
| Relamorelin | Synthetic agonist (C43H50N8O5S, 791.0) | No Drugs@FDA record | Not named; the class is not limited to named examples |
| Ipamorelin, GHRP-2, GHRP-6, hexarelin | Peptides of 5 or 6 amino acids | No FDA approval | Named in S2.2.4 |
Class S2.2.4 of the World Anti-Doping Agency’s 2026 Prohibited List names lenomorelin (ghrelin) itself among the growth hormone secretagogues, with anamorelin, capromorelin, ibutamoren (MK-677), ipamorelin, macimorelin and tabimorelin, and lists the GHRPs alongside them. They are banned at all times, in and out of competition.
Sources: PubChem CID 9828911, 9804938, 44251769; PubMed 33382205 (Wakabayashi and colleagues, 2021, on the Japanese approval of anamorelin); Drugs@FDA NDA205598 and openFDA searches of 3 November 2026; WADA 2026 Prohibited List as published in the Dutch Treaty Series (Trb. 2026, 25). Read 2 to 3 November 2026.
Ghrelin-receptor peptides sold for research
The four GHRPs in the table are sold as research peptides. None has an FDA approval, and a product labelled research use only is labelled not for human use. Our page on what research peptides are explains that label, and each guide sets out one compound’s identity, research history and regulatory record.
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 is ghrelin?
Ghrelin is a peptide hormone of 28 amino acids, made mainly in the stomach. MeSH, the U.S. National Library of Medicine's subject index, describes it as an acylated, orexigenic (appetite-stimulating) peptide that binds the growth hormone secretagogue receptor. It does two things that UniProt records: it makes the pituitary release growth hormone, and it increases appetite and food intake, which is why it is often called the hunger hormone.
Is ghrelin a peptide or a protein?
A peptide. Mature ghrelin is a single chain of 28 amino acids, GSSFLSPEHQRVQQRKESKKPPAKLQPR, and PubChem gives the acylated human form a molecular weight of 3,370.9. It is cut from a precursor protein of 117 amino acids that also yields a second peptide, obestatin.
Why does ghrelin carry a fatty acid?
Because without it ghrelin cannot switch on its receptor. An enzyme called ghrelin O-acyltransferase (GOAT, gene MBOAT4) attaches an eight-carbon fatty acid, an octanoyl group, to the serine at position 3; six- and ten-carbon versions also occur. UniProt records that this acylation is essential for activating the growth hormone secretagogue receptor. Ghrelin without the fatty acid is called des-acyl ghrelin.
What is the difference between ghrelin and leptin?
They work in opposite directions on appetite and come from different places. Ghrelin is a 28-amino-acid peptide from the stomach that UniProt records as increasing food intake; leptin is a 146-amino-acid hormone, mainly from fat tissue, that UniProt records as decreasing it. They also act on different receptors: ghrelin on GHS-R1a, leptin on the leptin receptor, LEPR.
What is obestatin?
Obestatin is a 23-amino-acid peptide cut from the same precursor as ghrelin, ending in a leucine amide. It was described in Science in 2005 as opposing ghrelin's effect on food intake. UniProt marks that appetite-reducing role as inferred by similarity rather than shown directly in humans.
What does ghrelin have to do with growth hormone?
Ghrelin is the natural ligand of the growth hormone secretagogue receptor on the pituitary and hypothalamus, and binding it releases growth hormone. Synthetic growth hormone-releasing peptides (GHRPs) such as GHRP-6 were made before ghrelin was found in 1999, which is why the receptor is named after the drugs rather than the hormone. Our growth hormone peptides page sets out both groups.
Are there medicines that act like ghrelin?
Yes, but none is a U.S.-approved ghrelin medicine today. Anamorelin, a small molecule taken by mouth, was approved in Japan on 11 December 2020 for cachexia in four cancers and was not approved in Europe. Macimorelin (Macrilen), another small molecule, was approved by FDA in 2017 to diagnose adult growth hormone deficiency and is now listed as discontinued. A search of Drugs@FDA on 3 November 2026 returned no record for ghrelin itself, its INN lenomorelin, anamorelin or relamorelin.
Is ghrelin banned in sport?
Yes. Class S2.2.4 of the World Anti-Doping Agency's 2026 Prohibited List names lenomorelin (ghrelin) and its mimetics, including anamorelin, ibutamoren (MK-677), ipamorelin and macimorelin, together with the GHRPs, and bans them at all times.
Is this medical advice?
No. This page explains what ghrelin is, from public scientific and regulatory sources. It gives no diet, dose, schedule, 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: UniProt Q9UBU3, Q96T53, Q92847, P41159; MeSH D054439; PubChem CID 16133832, 9828911, 9804938, 44251769; PubMed 10604470, 16284174, 18443287, 33382205; Drugs@FDA via openFDA; WADA 2026 Prohibited List. Read 2 to 3 November 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.