Ipamorelin.
Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) belonging to the growth hormone-releasing peptide (GHRP) class, sometimes described as a "third-generation" GHRP.
Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) belonging to the growth hormone-releasing peptide (GHRP) class, sometimes described as a "third-generation" GHRP. Ipamorelin is research / preclinical, and PepCue grades its published evidence F tier (33/100). This is a research reference, not medical or dosing advice.
What it is
Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) belonging to the growth hormone-releasing peptide (GHRP) class, sometimes described as a "third-generation" GHRP. Derived from the earlier secretagogue GHRP-1, it acts as a ghrelin mimetic and was characterized by Novo Nordisk researchers in the late 1990s as the first GHRP-receptor agonist with selectivity for growth hormone (GH) release approaching that of GHRH. It has no approved therapeutic indication and exists as an investigational/research compound.
How it works
Ipamorelin is a selective agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the same G-protein-coupled receptor activated by the endogenous hormone ghrelin. Binding at the pituitary (and hypothalamus) triggers GH release through a GHRP-like pathway distinct from, but synergistic with, GHRH signaling; pharmacological profiling with GHRH and GHRP antagonists showed its action is mediated via the GHRP-type receptor rather than the GHRH receptor. Its defining feature is selectivity: in the original characterization it released GH with potency comparable to GHRP-6 but, unlike older GHRPs, did not meaningfully raise ACTH, cortisol, FSH, LH, prolactin, or TSH, even at doses far above the ED50 for GH release.
Mechanism pathways
Acting on the ghrelin / GH-secretagogue receptor, a pathway separate from GHRH.
The growth hormone secretagogue receptor, GHS-R1a, is a G-protein-coupled receptor expressed on pituitary somatotrophs and in hypothalamic nuclei. Its natural ligand is ghrelin, the stomach-derived hormone associated with hunger. Activation raises growth hormone through a route entirely separate from GHRH: it acts directly on somatotrophs, and it also suppresses hypothalamic somatostatin tone, effectively releasing the brake at the same time as pressing the accelerator. This dual action is why compounds at this receptor and GHRH analogs are often studied together, since combining them produces a larger growth hormone response than either produces alone. The history here is unusual. The synthetic peptides in this group were developed in the 1980s and 1990s by working backwards from observed growth hormone release, years before ghrelin itself was identified in 1999. They were the pharmacological tools that led researchers to the receptor. They are therefore best understood as synthetic ghrelin mimetics that happened to be discovered before the hormone they mimic. Members of this group differ chiefly in selectivity, which is the practical distinction that matters most. GHS-R1a activation is not confined to growth hormone. Because the receptor sits on cells that also govern prolactin and adrenocorticotropic hormone release, and because ghrelin signalling drives appetite and influences gastric motility, several of these compounds raise cortisol and prolactin and increase hunger alongside the intended growth hormone effect. Others were specifically designed to avoid that, producing a comparatively clean growth hormone response with minimal spillover onto the other axes. Some also show additional activity at the CD36 receptor, which has been studied in cardiac contexts. Honest assessment of clinical relevance: the acute receptor pharmacology is well characterised, including in short human studies where growth hormone reliably rises after administration. That is proof of mechanism. What does not exist for this class is proof of benefit. No compound in this group is an approved medicine, controlled trials of sustained use with body composition or clinical endpoints are essentially absent, and material sold under these names is unregulated research-grade product of uncertain content. Growth hormone secretagogues are also prohibited in sport by anti-doping authorities. A further consideration specific to this receptor is desensitisation: sustained agonism at a G-protein-coupled receptor commonly reduces its responsiveness over time, so the acute hormonal response observed in a short study is not a reliable guide to what happens with continued use.
The evidence
The foundational evidence is preclinical: Raun et al. (Eur J Endocrinol, 1998) characterized ipamorelin in rats and isolated pituitary cells, establishing GH selectivity over ACTH/cortisol and other pituitary hormones. Subsequent animal work explored non-endocrine effects via GHS-R1a; for example, Venkova et al. (J Pharmacol Exp Ther, 2009) reported prokinetic/anti-ileus activity in a rodent model of postoperative ileus. The principal human data come from a single industry-sponsored (Helsinn Therapeutics) randomized, double-blind, placebo-controlled proof-of-concept trial in bowel-resection patients (Beck et al., Int J Colorectal Dis, 2014; ClinicalTrials.gov NCT00672074), where the primary composite gastrointestinal-recovery endpoint did not reach statistical significance, though some secondary measures trended favorably. There are no large, controlled human trials demonstrating efficacy for muscle growth, anti-aging, fat loss, bone density, or body composition in people; widely repeated claims in those areas rest on mechanism and animal data, not human outcome trials, and the postoperative-ileus program did not advance to Phase III.
The evidence, in brief
A selective pentapeptide GH secretagogue that raises growth hormone without meaningfully changing prolactin, ACTH, or cortisol. Human data are limited to small, short-term pharmacology studies in healthy volunteers; it has no FDA approval and no large or long-term efficacy/safety trials; it remains a research compound.
- Raun K et al.: Ipamorelin, the first selective growth hormone secretagogueEur J Endocrinol, 1998 (PMID 9849822)
Evidence maturity
An evidence-only reading: approval status, human vs preclinical data, mechanism and safety. Popularity never raises it. Research file #033
Mostly preclinical or mechanistic; little human data.
Findings come mainly from animal models, not people.
Claim receipts
Popular claims about Ipamorelin, checked against the state of the evidence. The verdict describes evidence maturity, never an invented study result.
Stimulates GH release, but long-term human safety is not established; research-only.
Safety profile
Human safety data are limited to small, short-duration trials; the bowel-resection study used intravenous administration in a hospital setting and did not establish a long-term safety profile. As a GH/IGF-1-axis stimulant, plausible class-related concerns include effects on insulin sensitivity and blood glucose, fluid retention, and theoretical risks tied to chronically elevated GH/IGF-1 (e.g., relevant to people with cancer or active proliferative conditions), though these have not been well characterized for ipamorelin specifically in humans. Because much non-clinical material is produced as unregulated "research chemical" powder, real-world risks also include impurity, mislabeling, and lack of sterility/quality control. Long-term consequences of repeated use in humans are essentially unknown.
Compound notes
- Ipamorelin is a selective growth-hormone secretagogue: a ghrelin/GH-secretagogue-receptor (GHS-R) agonist that prompts the pituitary to release growth hormone.
- Its selling point is selectivity: it stimulates GH release with minimal effect on cortisol or prolactin, unlike older GHRPs such as GHRP-6 or GHRP-2.
- It acts on the ghrelin-receptor pathway, which is distinct from (and complementary to) the GHRH pathway used by GHRH analogs.
Ipamorelin works on the ghrelin/GHS receptor; GHRH analogs (sermorelin, CJC-1295, tesamorelin) work on the GHRH receptor. These are two separate levers on the same GH axis.
- Not FDA-approved; research-only.
- Long-term human safety is not established.
Regulatory status
Ipamorelin is not approved by the FDA (or other major regulators) for any indication; it remains an investigational/research-use compound and was the subject of FDA pharmacy-compounding review activity rather than drug approval. It is prohibited in sport by the World Anti-Doping Agency at all times as a growth hormone secretagogue under category S2 (Peptide Hormones, Growth Factors, and Mimetics).
Sold research-use-only; human evidence is limited or preclinical.
By the numbers
- 01Pentapeptide Aib-His-D-2-Nal-D-Phe-Lys-NH2, derived from GHRP-1; a ghrelin/GHS-R1a agonist
- 02Described as the first GHRP-receptor agonist with GH-release selectivity approaching GHRH (Raun et al., 1998)
- 03Distinguished from older GHRPs by not significantly raising ACTH, cortisol, or prolactin in the original characterization
- 04Best human evidence is one placebo-controlled proof-of-concept trial in bowel-resection patients (NCT00672074) that missed its primary endpoint
- 05Not FDA-approved for any indication; research/investigational status only
- 06Prohibited at all times in sport by WADA (category S2) as a GH secretagogue
Ipamorelin: research formats
Choose the format you are researching to see route-specific notes.
Most selective GHRP; commonly combined with a GHRH analog (CJC-1295) in the same injection.
Ipamorelin is sold as a 2 mg or 5 mg lyophilized vial. Reconstituting 2 mg with 2.0 mL BAC water gives 1,000 mcg/mL. Ipamorelin acts at the ghrelin/GHS-R1a receptor; when combined with CJC-1295 in the same syringe, both compounds are typically drawn into one injection.
Drawing ipamorelin and CJC-1295 no-DAC into the same syringe is standard practice in research contexts, since they are chemically compatible. Draw one first, then add the second to the same needle.
Sources
Every factual claim above resolves to a real, published source.
- Ipamorelin, the first selective growth hormone secretagogueEuropean Journal of Endocrinology, 1998; Raun K, et al.; PMID 9849822
- Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patientsInternational Journal of Colorectal Disease, 2014; Beck DE, et al.; PMID 25331030 (NCT00672074)
- Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileusJournal of Pharmacology and Experimental Therapeutics, 2009; Venkova K, et al.; PMID 19289567
- WADA Prohibited List (category S2: Peptide Hormones, Growth Factors, Related Substances and Mimetics)World Anti-Doping Agency, current Prohibited List
Cite this page
PepCue. “Ipamorelin: the evidence.” PepCue, reviewed June 1, 2026. https://www.pepcue.app/p/ipamorelin.
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