Ipamorelin

What Is Ipamorelin?

Ipamorelin is a synthetic five-residue peptide that stimulates growth hormone (GH) release from the pituitary by acting at the receptor for GH-releasing peptides, the same receptor targeted by ghrelin. Its developers described it in 1998 as the first selective GH secretagogue, because it released GH without the ACTH and cortisol increases seen with related peptides.^[1]

Later animal studies describe ipamorelin as a ghrelin mimetic and growth hormone secretagogue receptor 1a (GHS-R1a) agonist.^[2][3] It differs from growth hormone-releasing hormone (GHRH) analogues such as sermorelin and CJC-1295, which act through a separate receptor.

Ipamorelin is also discussed in sports medicine and orthopedic reviews as one of several unapproved peptides marketed for recovery and performance, often in combination with CJC-1295. These reviews consistently note that human data are limited.^[4][5]

Chemical Structure and Molecular Identity

Ipamorelin is a pentapeptide amide with the molecular formula C38H49N9O5 and a molecular weight of 711.9 g/mol (PubChem CID 9831659). Its sequence is Aib-His-D-2-Nal-D-Phe-Lys-NH2.

Residues

• Aib: 2-aminoisobutyric acid (2-methylalanine), a non-proteinogenic residue at the N-terminus
• His: L-histidine
• D-2-Nal: 3-(2-naphthyl)-D-alanine, a non-natural aromatic D-amino acid
• D-Phe: D-phenylalanine
• Lys-NH2: L-lysine with a C-terminal amide

Because three of its five residues are non-standard or D-configured, ipamorelin cannot be written as a standard one-letter sequence. PubChem lists the InChIKey NEHWBYHLYZGBNO-BVEPWEIPSA-N, the CAS number 170851-70-4, the UNII Y9M3S784Z6 and the development code NNC 26-0161.

At roughly 0.7 kDa, ipamorelin is far smaller than the GHRH analogues it is often studied alongside, which weigh more than 3,300 g/mol. PubChem’s computed XLogP of 1.8 reflects its aromatic naphthyl and phenyl side chains.

Comparison with related secretagogues

Research History and Development

Ipamorelin came out of a major medicinal chemistry programme on GH-releasing peptides and was first described in 1998. It was identified within a series of compounds that lack the central Ala-Trp dipeptide of GH-releasing peptide-1 (GHRP-1).^[1]

The founding paper profiled ipamorelin in primary rat pituitary cells, anesthetized rats and conscious swine, benchmarking it against GHRP-6 and GHRP-2.^[1] A 1999 study then examined its effects on longitudinal bone growth in adult female rats, framing the open question of whether GH secretagogues might have a role in children with growth retardation.^[6]

More recent work has used ipamorelin as a reference ghrelin agonist in other species and models, including cisplatin-induced weight loss in ferrets and the reproductive axis of a cichlid fish.^[2][3] In 2026, it also featured in several reviews of peptides marketed directly to patients and athletes.^[7][8][9]

Mechanisms Studied in Research

Ipamorelin stimulates GH release through a GHRP-like receptor rather than the GHRH receptor, a mechanism established using selective GHRP and GHRH antagonists. In this respect it behaves like GHRP-6.^[1]

Selectivity

In conscious swine, none of the secretagogues tested, including ipamorelin, GHRP-6 and GHRP-2, changed plasma FSH, LH, prolactin or TSH. GHRP-6 and GHRP-2 raised ACTH and cortisol, but ipamorelin did not raise either to levels significantly different from those after GHRH stimulation.^[1]

Ghrelin receptor effects beyond GH

As a GHS-R1a agonist, ipamorelin has been studied for effects tied to ghrelin signaling, including feeding, body weight and gut motility. In isolated ferret ileum, it inhibited electrically stimulated contractions by 54.4% with a half-maximal inhibitory concentration of 11.7 µM.^[2] In tilapia, it increased food intake and was associated with higher serum luteinizing hormone and 11-ketotestosterone. GnRH-immunoreactive fibers in the hypothalamus and pituitary did not differ between groups, while androgen receptor protein rose at the higher dose level, pointing to effects at both pituitary and testicular levels.^[3]

Proposed tissue effects

An orthopedic review groups ipamorelin with other secretagogues proposed to activate IGF-1 signaling and satellite cell repair, while noting a lack of clinical trials.^[7]

Key Findings From Published Studies

Most published findings on ipamorelin come from in vitro and animal studies showing GH release comparable to GHRP-6, high selectivity, and effects on bone growth, body weight and reproduction in specific models. Controlled human data are not represented in the sources compiled for this page.

Potency in vitro and in vivo

In primary rat pituitary cells, ipamorelin released GH with a potency and efficacy similar to GHRP-6 (EC50 1.3 nmol/L and Emax 85%, versus 2.2 nmol/L and 100%). Potency and efficacy were also comparable to GHRP-6 in anesthetized rats and conscious swine, while GHRP-2 showed higher potency but lower efficacy in swine.^[1]

Bone growth in rats

In adult female rats treated for 15 days, ipamorelin dose-dependently increased longitudinal bone growth rate in the tibia from 42 µm/day in the vehicle group to 44, 50 and 52 µm/day across treatment groups, and increased body weight gain. Total IGF-I, IGF-binding proteins and serum bone turnover markers did not change, and pituitary GH content was unaffected. After treatment, the plasma GH response to an ipamorelin challenge was marginally reduced, while the response to GHRH was unchanged.^[6]

Ferret and fish models

In ferrets given cisplatin, ipamorelin did not affect acute or delayed emesis but reduced cisplatin-induced weight loss by about 24% at the end of the delayed phase. The comparator ghrelin mimetic anamorelin reduced weight loss by a similar margin, but only anamorelin given directly into the brain reduced acute emesis, which the authors attributed to a central mechanism.^[2] In male tilapia treated for 21 days, ipamorelin acetate increased counts of primary and secondary spermatocytes and early spermatids at both dose levels tested.^[3]

Combination and review data

A review reports that CJC-1295 combined with ipamorelin improved maximum tetanic tension in mice with glucocorticoid-induced muscle loss, a finding limited to animal studies.^[5] A 2026 scoping review covering ipamorelin found that 67% of identified musculoskeletal publications used preclinical animal models and that human studies were few and mostly lacked robust controls.^[8]

Because ipamorelin contains three non-standard or D-configured residues, researchers typically confirm identity and purity with HPLC and mass spectrometry data on a certificate of analysis.

Regulatory and Research Status

Ipamorelin is not approved by the US Food and Drug Administration for any indication. Sports medicine reviews place it among unapproved peptides sold in a “gray market” largely outside regulatory oversight, where rigorous human safety data are scarce. The review also discusses the placebo effect as a mediator of reported peptide benefits and how social media amplifies it.^[4]

Growth hormone secretagogues, including ipamorelin, are prohibited in sport under the World Anti-Doping Agency Prohibited List. A 2026 doping review notes that peptides such as ipamorelin are marketed as more selective and ostensibly safer alternatives to anabolic steroids, that products in unregulated supply chains are often mislabeled or contaminated, and that detection remains analytically challenging. The same review lists potential risks emerging across the peptide class, including cardiovascular strain, insulin resistance, dyslipidemia and psychiatric instability.^[9] A scoping review adds that such peptides are often perceived as low risk despite the absence of efficacy or safety data for many of them.^[8]

The research base remains dominated by animal pharmacology. Reviews published in 2026 describe preclinical results as promising but stress the lack of clinical trials, and the 1999 bone growth study itself concluded that any role for GH secretagogues in growth retardation would require demonstration in clinical studies.^[7][8][6]