Ipamorelin is a synthetic pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, developed at Novo Nordisk under the code NNC 26-0161 and described in its discovery paper as the first selective growth hormone secretagogue . It is an agonist at the growth hormone secretagogue receptor. It is a laboratory reagent and is not approved by the U.S. Food and Drug Administration for any indication.

Ipamorelin Research, Specifications & Scientific Information

Ipamorelin is a synthetic pentapeptide agonist at the growth hormone secretagogue receptor, described in its discovery paper as the first selective growth hormone secretagogue because it released growth hormone in swine without measurable release of ACTH or cortisol. It is not approved by the FDA for any indication.

By Elegance Peptides Editorial TeamPublished September 22, 2026Updated September 22, 2026

Category: GHRH analogues and GH secretagogues

Introduction

Ipamorelin was introduced to the literature in 1998 under a claim that is unusual for being falsifiable: that it was the first selective growth hormone secretagogue ^[2]. The secretagogues that preceded it released growth hormone, but they also raised ACTH and cortisol, and that side of their pharmacology was the obstacle to developing them. The Novo Nordisk chemistry programme that produced ipamorelin set out from a series of compounds lacking the central Ala-Trp dipeptide of growth hormone-releasing peptide 1, and arrived at a pentapeptide that released growth hormone with potency comparable to the hexapeptides while leaving ACTH and cortisol unmoved in swine.

It is a synthetic molecule of five residues, three of which are not standard amino acids. It has a published human pharmacokinetic study, two completed phase 2 trials in an indication that has nothing to do with growth, and no approval anywhere. This page sets out what was measured, in which species, and what the selectivity claim does and does not cover.

What Is Ipamorelin?

Ipamorelin is a synthetic pentapeptide: Aib-His-D-2-Nal-D-Phe-Lys-NH2. It acts at the growth hormone secretagogue receptor — the receptor identified in pituitary and hypothalamus in 1996 as the target of the synthetic secretagogues ^[1], and shown three years later to be the receptor for ghrelin, an acylated peptide from the stomach ^[5].

That receptor is the dividing line in this catalogue. Compounds such as sermorelin, tesamorelin and CJC-1295 are analogues of growth hormone-releasing hormone and act at the GHRH receptor, a class B1 G protein-coupled receptor. Ipamorelin, GHRP-2 and GHRP-6 act at the growth hormone secretagogue receptor, a class A receptor with a different signalling profile. The two families are often listed together because both raise growth hormone; they are not structural or pharmacological relatives.

Ipamorelin is not an approved medicine. It originated at Novo Nordisk A/S under the code NNC 26-0161 and was later carried into clinical trials by Helsinn Therapeutics in postoperative ileus, where development stopped after phase 2.

Ipamorelin Specifications

Compound name: Ipamorelin
Full chemical name: 2-Methylalanyl-L-histidyl-3-(2-naphthyl)-D-alanyl-D-phenylalanyl-L-lysinamide
Aliases: NNC 26-0161, Aib-His-D-2-Nal-D-Phe-Lys-NH2, GHRP-receptor agonist pentapeptide
Development code: NNC 26-0161
CAS number: 170851-70-4
PubChem CID: 9831659
UNII: Y9M3S784Z6
Compound type: Synthetic pentapeptide
Peptide family: Growth hormone secretagogues (ghrelin receptor agonists)
Amino acid sequence: Aib-His-D-2-Nal-D-Phe-Lys-NH₂
Sequence length: 5 residues
Molecular formula: C38H49N9O5
Molecular weight: 711.85 g/mol
Primary target: Growth hormone secretagogue receptor 1a (GHS-R1a, the ghrelin receptor)
Secondary targets: Not publicly characterised
Receptor family: Class A (rhodopsin-like) G protein-coupled receptors
Agonist / antagonist status: Agonist at the growth hormone secretagogue receptor

Ipamorelin cannot be written in standard single-letter code, which is why the sequence is given in three-letter notation with the non-standard residues named. Position 1 is alpha-aminoisobutyric acid (Aib), a methylated alanine that is not one of the twenty proteinogenic amino acids; position 3 is the D-enantiomer of 3-(2-naphthyl)alanine; position 4 is D-phenylalanine; and the C-terminus is an amide rather than a free acid. Only histidine at position 2 and lysine at position 5 are ordinary L-amino acids. The molecule was identified within a chemistry programme at Novo Nordisk from a series of compounds lacking the central Ala-Trp dipeptide of growth hormone-releasing peptide 1, which is why it is a pentapeptide where the earlier secretagogues in this family are hexapeptides. The identifiers shown are those recorded in the FDA/NCATS Global Substance Registration System under UNII Y9M3S784Z6 and in PubChem under compound identifier 9831659, whose molecular formula and mass agree with the supplier catalog values. Any figure on this page is a reference value: the certificate of analysis supplied with a laboratory order is the record for a given lot.

Values that a public register does not carry are shown as not publicly characterised rather than estimated. Identifiers are reference values; the certificate of analysis supplied with a laboratory order is the record for a given lot.

How Does Ipamorelin Work?

The growth hormone secretagogue receptor sits on pituitary somatotrophs and in the hypothalamus, and its natural ligand is ghrelin ^{[1, 5]}. It is a class A, rhodopsin-like G protein-coupled receptor coupling principally through Gq and phospholipase C — a different transduction route from the Gs/cyclic AMP pathway used by the growth hormone-releasing hormone receptor. That difference is why secretagogues at the two receptors produce additive rather than redundant growth hormone release, a point developed at length in the review literature on this compound class ^[7].

Ipamorelin's own contribution to that literature is the question of what else a secretagogue engages. Ghrelin receptor signalling in the hypothalamus is involved in more than growth hormone: it is the pathway through which ghrelin influences feeding behaviour, and in the pituitary the earlier hexapeptides drove corticotroph output alongside somatotroph output. A molecule that separates those outputs is pharmacologically informative regardless of whether it becomes a medicine.

Ipamorelin Mechanism of Action

In vitro research

In primary rat pituitary cells, ipamorelin released growth hormone with an EC50 of 1.3 ± 0.4 nmol/l and an Emax of 85 ± 5%, against 2.2 ± 0.3 nmol/l and 100% for GHRP-6 — comparable potency and slightly lower maximal effect ^[2].

The receptor assignment was made pharmacologically rather than assumed. The discovery work profiled ipamorelin against both GHRP antagonists and growth hormone-releasing hormone antagonists, and the pattern of blockade placed its action at the GHRP-like receptor ^[2]. That receptor had been cloned two years earlier from pituitary and hypothalamus and characterised as a G protein-coupled receptor mediating the action of the synthetic secretagogues ^[1].

A separate in vitro observation comes from much later work on gastrointestinal effects: in isolated ferret ileum, ipamorelin inhibited contractions evoked by electrical field stimulation, an effect it shared with the clinically developed ghrelin mimetic anamorelin ^[10].

What Is Ipamorelin Being Researched For?

Published and registered research on ipamorelin falls into four groups:

Growth hormone secretagogue pharmacology and selectivity — the discovery work in cells, rats and swine ^[2].
Human pharmacokinetics and the growth hormone response — one published volunteer study ^[4].
Postoperative ileus and gastrointestinal motility — rodent models followed by two registered phase 2 trials ^{[8, 9, 11, 12]}.
Bone and skeletal models in rodents — longitudinal growth and glucocorticoid-exposed bone ^{[3, 6]}.

The clinical work is research into a pharmaceutical product candidate conducted by its sponsor under a protocol. None of it is research into, or evidence about, research-grade material supplied for laboratory use.

Human Research on Ipamorelin

Human clinical research

Results from pharmaceutical clinical trials describe the investigational material and populations used in those studies and should not be interpreted as establishing the effects of research-grade materials offered for laboratory use.

Pharmacokinetics and growth hormone response in healthy volunteers

Population. Healthy male volunteers, eight at each of five levels ^[4].

Endpoint and duration. An escalating-amount trial of five 15-minute infusion rates — 4.21, 14.02, 42.13, 84.27 and 140.45 nmol/kg — with concentrations of ipamorelin and of growth hormone measured throughout ^[4].

Result. Pharmacokinetic parameters were proportional to the amount administered: terminal half-life approximately 2 hours, clearance 0.078 L/h/kg, steady-state volume of distribution 0.22 L/kg. Growth hormone release was a single episode peaking at 0.67 hours and declining exponentially to negligible concentrations at every level tested. The concentration required for half-maximal growth hormone stimulation was 214 nmol/L ^[4].

Limitations. A single-administration pharmacology study in healthy men, designed to model the concentration-response relationship. It measured a hormone, not a clinical outcome, and it says nothing about repeated administration.

Phase 2 trials in postoperative ileus

Population. Two trials sponsored by Helsinn Therapeutics. The first enrolled 117 participants; the second enrolled 320 participants following small or large bowel resection with primary anastomosis ^{[11, 12]}.

Endpoint and duration. Both were phase 2, double-blind and placebo-controlled; the first was a multiple-administration safety and efficacy study, the second a finding study across several amounts ^{[11, 12]}.

Result. Both are recorded in the public trial register as completed. No results for either have been published in the peer-reviewed literature, and none are summarised here. A completed trial without published results supports no conclusion in either direction.

Limitations. The absence of published outcomes is itself the limitation. Development did not continue past phase 2, and the reason has not been stated in any source that could be verified.

Preclinical Research on Ipamorelin

Animal research

The discovery study tested the compound in two species. In pentobarbital-anaesthetised rats it released growth hormone with an ED50 of 80 ± 42 nmol/kg and an Emax of 1545 ± 250 ng GH/ml, against 115 ± 36 nmol/kg and 1167 ± 120 ng GH/ml for GHRP-6. In conscious swine the ED50 was 2.3 ± 0.03 nmol/kg with an Emax of 65 ± 0.2 ng GH/ml plasma, again close to GHRP-6 at 3.9 ± 1.4 nmol/kg and 74 ± 7 ng GH/ml; GHRP-2 was more potent but less efficacious in the same comparison ^[2].

The selectivity result came from the swine work. None of the secretagogues tested altered plasma FSH, LH, prolactin or TSH. GHRP-6 and GHRP-2 both raised plasma ACTH and cortisol. Ipamorelin did not — and the authors emphasised that this held even at amounts more than 200-fold above its ED50 for growth hormone release ^[2]. This is the entire evidential basis for the word "selective" in the compound's name, and it is a finding in swine.

Two rat studies examined bone. In the first, ipamorelin induced longitudinal bone growth in rats ^[3]. In the second, it counteracted a glucocorticoid-induced decrease in bone formation in adult rats ^[6]. Both are rodent skeletal models, and neither has a human counterpart for this compound.

Findings described in this section were observed in animals, and nothing in them establishes anything about humans.

Other Areas of Ipamorelin Research

Animal research

The indication ipamorelin was actually carried into clinical trials for is gastrointestinal, not endocrine, and the preclinical case for it was built in rodents. A 2009 study reported efficacy in a rodent model of postoperative ileus ^[8], and a later study in the same laboratory examined gastric dysmotility specifically within that model ^[9]. The rationale is the ghrelin receptor's role in gastric emptying and enteric motor control rather than anything to do with growth hormone.

A more recent ferret study asked whether ghrelin mimetics could offset the anorexia and weight loss that follow cisplatin. Ferrets received ipamorelin or anamorelin at 1 to 3 mg/kg intraperitoneally before cisplatin and then every 24 hours, with behaviour recorded for up to 72 hours and food and water consumption measured daily; both compounds also inhibited electrically evoked contractions of isolated ferret ileum ^[10]. The study's comparative finding was that anamorelin, not ipamorelin, additionally showed anti-emetic effects through a central mechanism.

These are animal models of clinical problems, run in species chosen for their emetic physiology rather than their similarity to humans in any other respect. Findings described in this section were observed in animals.

Current Research Status

Regulatory status (United States): Not approved. Ipamorelin has not been approved by the U.S. Food and Drug Administration for any indication.
Investigational status: Originated at Novo Nordisk A/S and later studied by Helsinn Therapeutics. Two phase 2 trials in postoperative ileus were registered and are recorded as completed; no phase 3 programme and no approval followed, and no active clinical development has been identified.
Highest research phase reached: Phase 2 (completed; results not published in the peer-reviewed literature)
Approved uses: None
Approval is compound-specific: No

Status as of September 22, 2026. This block is rendered from maintained fields, not from prose, so it cannot go stale in one place and stay current in another.

Chemical & Molecular Characteristics

Ipamorelin is a pentapeptide that cannot be written in single-letter code, and the reason is instructive: three of its five residues are not proteinogenic amino acids.

The residues. Position 1 is alpha-aminoisobutyric acid, a methylated alanine with no single-letter representation. Position 2 is L-histidine. Position 3 is the D-enantiomer of 3-(2-naphthyl)alanine. Position 4 is D-phenylalanine. Position 5 is L-lysine, and the chain terminates in an amide.

The identifiers agree. CAS registry number 170851-70-4, UNII Y9M3S784Z6 and PubChem compound identifier 9831659 all resolve to this substance, and the molecular formula C38H49N9O5 and molecular weight 711.85 g/mol are consistent between those registers and the supplier catalog. That is a stronger identifier position than most compounds in this family, several of which have no register record at all.

The design logic is visible in the structure. D-amino acids at positions 3 and 4 and the C-terminal amide are the standard devices for resisting proteolysis; the non-standard residue at position 1 blocks aminopeptidase attack at the N-terminus. The resulting molecule nonetheless has a terminal half-life of roughly two hours in humans ^[4] — short, by design, relative to the albumin-binding GHRH analogues.

Analytical Specifications

Physical form: Lyophilized powder
Appearance: White to off-white lyophilized solid
Lot number: RP-2607-046
Tested purity: ≥99% by HPLC
Storage: −20 °C, protect from light, desiccate

Analytical figures are lot-specific. Fields the catalog does not carry for the current lot are omitted rather than filled with a typical value. The certificate of analysis and the safety data sheet for the exact lot supplied are provided with a laboratory order; no purity figure on this page is a substitute for that document.

Frequently Asked Questions

What is ipamorelin?

Ipamorelin is a synthetic pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, developed at Novo Nordisk under the code NNC 26-0161 and described in its discovery paper as the first selective growth hormone secretagogue ^[2]. It is an agonist at the growth hormone secretagogue receptor. It is a laboratory reagent and is not approved by the U.S. Food and Drug Administration for any indication.

How does ipamorelin work?

Through the growth hormone secretagogue receptor, the pituitary and hypothalamic receptor identified in 1996 and later shown to be the receptor for the stomach-derived peptide ghrelin ^{[1, 5]}. Profiling with GHRP and GHRH antagonists placed ipamorelin’s action at the GHRP-like receptor rather than at the growth hormone-releasing hormone receptor ^[2].

Why is ipamorelin described as selective?

Because of what it did not do in the discovery pharmacology. In conscious swine, none of the secretagogues tested altered plasma FSH, LH, prolactin or TSH, but GHRP-6 and GHRP-2 both raised ACTH and cortisol, while ipamorelin did not — at amounts more than 200-fold above its ED50 for growth hormone release ^[2]. That finding is the basis of the “selective” description and it was made in swine, not in people.

What receptor does ipamorelin target?

The growth hormone secretagogue receptor 1a, a class A G protein-coupled receptor cloned from pituitary and hypothalamus ^[1]. This is a different receptor from the one engaged by growth hormone-releasing hormone analogues such as sermorelin and CJC-1295, which is why the two families are pharmacologically distinct.

Is ipamorelin FDA approved?

No. Ipamorelin has not been approved by the U.S. Food and Drug Administration for any indication. Two phase 2 trials in postoperative ileus were registered and completed, but no phase 3 programme and no approval followed ^{[11, 12]}.

Has ipamorelin been studied in humans?

Yes. A published trial in healthy male volunteers characterised its pharmacokinetics and the growth hormone response across five ascending 15-minute infusion rates, with eight participants at each level ^[4]. Two phase 2 trials in postoperative ileus, enrolling 117 and 320 participants, are recorded as completed in the public trial register ^{[11, 12]}; results for those two have not appeared in the peer-reviewed literature.

How does ipamorelin differ from GHRP-6 and GHRP-2?

All three act at the same receptor, and in the discovery comparison ipamorelin released growth hormone from rat pituitary cells with potency and efficacy similar to GHRP-6 ^[2]. The difference is structural and hormonal: ipamorelin is a pentapeptide identified from a series lacking the central Ala-Trp dipeptide of GHRP-1, and unlike GHRP-2 and GHRP-6 it did not raise ACTH or cortisol in swine ^[2].

What is the reported half-life of ipamorelin?

About two hours. In healthy male volunteers the terminal half-life was approximately 2 hours, with clearance of 0.078 L/h/kg and a steady-state volume of distribution of 0.22 L/kg; growth hormone release was a single episode peaking near 0.67 hours ^[4]. Those figures describe the material administered in that trial.

Scientific References

Howard AD, Feighner SD, Cully DF, et al.. A receptor in pituitary and hypothalamus that functions in growth hormone release Science (New York, N.Y.); 1996. PMID 8688086 doi:10.1126/science.273.5277.974
Raun K, Hansen BS, Johansen NL, et al.. Ipamorelin, the first selective growth hormone secretagogue European journal of endocrinology; 1998. PMID 9849822 doi:10.1530/eje.0.1390552
Johansen PB, Nowak J, Skjaerbaek C, et al.. Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats Growth hormone & IGF research : official journal of the Growth Hormone Research Society and the International IGF Research Society; 1999. PMID 10373343 doi:10.1054/ghir.1999.9998
Gobburu JV, Agersø H, Jusko WJ, et al.. Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers Pharmaceutical research; 1999. PMID 10496658 doi:10.1023/a:1018955126402
Kojima M, Hosoda H, Date Y, et al.. Ghrelin is a growth-hormone-releasing acylated peptide from stomach Nature; 1999. PMID 10604470 doi:10.1038/45230
Andersen NB, Malmlöf K, Johansen PB, et al.. The growth hormone secretagogue ipamorelin counteracts glucocorticoid-induced decrease in bone formation of adult rats Growth hormone & IGF research : official journal of the Growth Hormone Research Society and the International IGF Research Society; 2001. PMID 11735244 doi:10.1054/ghir.2001.0239
Smith RG. Development of growth hormone secretagogues Endocrine reviews; 2005. PMID 15814848 doi:10.1210/er.2004-0019
Venkova K, Mann W, Nelson R, et al.. Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus The Journal of pharmacology and experimental therapeutics; 2009. PMID 19289567 doi:10.1124/jpet.108.149211
Greenwood-Van Meerveld B, Tyler K, Mohammadi E, et al.. Efficacy of ipamorelin, a ghrelin mimetic, on gastric dysmotility in a rodent model of postoperative ileus Journal of experimental pharmacology; 2012. PMID 27186127 doi:10.2147/JEP.S35396
Lu Z, Ngan MP, Liu JYH, et al.. The growth hormone secretagogue receptor 1a agonists, anamorelin and ipamorelin, inhibit cisplatin-induced weight loss in ferrets: Anamorelin also exhibits anti-emetic effects via a central mechanism Physiology & behavior; 2024. PMID 39043357 doi:10.1016/j.physbeh.2024.114644
Safety and Efficacy of Ipamorelin for Management of Post-Operative Ileus 2008. NCT00672074
Safety and Efficacy of Ipamorelin Compared to Placebo for the Recovery of Gastrointestinal Function 2011. NCT01280344

Every identifier above is resolved against PubMed, Crossref or ClinicalTrials.gov at build time, and the title returned by the register is compared with the title stored here. A page does not publish if a reference fails to resolve.

Research-Use Information

For in vitro research use only. This material is a laboratory reagent. It is not a drug, food, dietary supplement, or cosmetic and is not for human or veterinary use, including ingestion, injection, or any other administration. No information on this page describes or implies any effect in humans or animals. Sold only to researchers under our Terms of Sale.