Research use only. This monograph is a scientific reference. It contains no dosing schedule, administration protocol, or medical guidance for human use. Dosing context is covered separately in a laboratory framing.
Ipamorelin is a synthetic pentapeptide and one of the most selective growth hormone (GH) secretagogues described in the literature. It was developed at Novo Nordisk under the code NNC 26-0161 and belongs to the growth hormone releasing peptide (GHRP) class of ghrelin receptor agonists. Its defining property, established in the original characterization by Raun and colleagues, is that it triggers a clean pulse of GH release without meaningfully raising adrenocorticotropic hormone (ACTH), cortisol, or prolactin [1].
Structure and physicochemistry
Ipamorelin has the amino acid sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2. It was engineered from growth hormone releasing peptide-1 (GHRP-1): the central Ala-Trp dipeptide was removed and an aminoisobutyric acid (Aib) residue was placed at the N-terminus to resist enzymatic breakdown [1]. The two D-amino acids and the C-terminal amide further improve metabolic stability. The molecular formula is C38H49N9O5 with a molar mass near 711.9 g/mol; the CAS (Chemical Abstracts Service number) registry number is 170851-70-4. For laboratory work the compound is usually supplied as a lyophilized acetate salt that is readily soluble in water.
Mechanism of action
Ipamorelin is a ghrelin mimetic. It binds and activates the growth hormone secretagogue receptor type 1a (GHS-R1a), a G-protein-coupled receptor expressed in the hypothalamus and the anterior pituitary. This receptor was identified by Howard and colleagues in 1996 as the target of an earlier generation of synthetic secretagogues, before its natural ligand was known [7]. That endogenous ligand, the acylated stomach peptide ghrelin, was isolated by Kojima and colleagues in 1999, which placed the whole GHRP class on a clear physiological footing [8]. When ipamorelin activates GHS-R1a on pituitary somatotrophs, it drives a discrete episode of GH secretion that resembles a natural secretory pulse in amplitude and duration. Pharmacological profiling with GHRP and GHRH antagonists showed that ipamorelin works through the GHRP-like (ghrelin) pathway rather than the GHRH receptor [1].
Selectivity
The feature that set ipamorelin apart from earlier peptides such as GHRP-6 and GHRP-2 is its selectivity. In the founding study, ipamorelin released GH with high potency and efficacy yet did not raise ACTH or cortisol above the levels seen after plain GHRH stimulation, and it did so even at doses far above those needed for maximal GH release [1]. This wide separation between the GH-releasing dose and the dose that touches the stress-hormone axis is the main reason ipamorelin became a reference tool for studying selective GH release.
Preclinical research
Most of what is known about ipamorelin comes from animal work. In young female rats, chronic administration increased body weight gain and preserved the ability of pituitary tissue to release GH, consistent with sustained secretagogue activity [1]. Two bone studies are frequently cited. Svensson and colleagues reported that ipamorelin and GHRP-6 increased tibial and vertebral bone mineral content in adult female rats, although the gain tracked the increase in body weight rather than raising bone density independently [4]. Andersen and colleagues showed that ipamorelin counteracted glucocorticoid-induced suppression of bone formation, with a roughly four-fold rise in periosteal bone formation rate when it was combined with the glucocorticoid, plus a measurable gain in muscle tension [5]. Separately, Venkova and colleagues found that ipamorelin accelerated gastric emptying and colonic transit in a rodent model of postoperative ileus, acting through a ghrelin-receptor mechanism that recruits cholinergic excitatory neurons [6]. These findings are informative, but they are animal data, and they do not by themselves establish clinical benefit in humans.
Human data
Human evidence for ipamorelin is limited and comes mainly from two lines of work. First, a phase 1 pharmacokinetic and pharmacodynamic study in healthy male volunteers characterized the dose-proportional pharmacokinetics and the single, transient GH pulse produced by an intravenous infusion [2]. Second, because of its ghrelin-like prokinetic action, ipamorelin was tested for postoperative ileus. A prospective, randomized, placebo-controlled proof-of-concept trial in patients recovering from bowel resection reported that ipamorelin accelerated the return of bowel function and was well tolerated, with a favorable safety profile [3]. It is important to be clear about scope. This proof-of-concept result did not translate into a marketed product. Ipamorelin was never granted marketing approval for any indication, and its clinical development was discontinued. There is no approved human use.
Pharmacokinetics
In the human phase 1 work, ipamorelin behaved predictably. After intravenous infusion the pharmacokinetics were dose-proportional across the tested range, with a terminal elimination half-life of about 2 hours, a clearance near 0.078 L/h/kg, and a steady-state volume of distribution around 0.22 L/kg [2]. The GH response was a single pulse that peaked well within the first hour and then declined to baseline, so the pharmacodynamic effect is short and self-limiting rather than a sustained elevation.
Regulatory and research status
Ipamorelin is an investigational peptide. It has no approved therapeutic indication in any major jurisdiction, its clinical program was halted, and it is not a licensed medicine. In practice it is used as a laboratory reference compound and a pharmacological probe for selective GH secretagogue activity and for ghrelin-receptor signaling.
Handling and storage
As with other peptides, the lyophilized powder is stored frozen, typically at -20 °C, protected from light and moisture. After reconstitution in sterile water the solution is kept refrigerated and repeated freeze-thaw cycles are avoided, since they degrade peptide integrity. These are laboratory handling notes, not directions for use in humans.
Research-use disclaimer
This page reports the published science on ipamorelin for research and laboratory use only. It is not medical advice, it does not endorse human administration, and it deliberately contains no dosing protocol. Ipamorelin is not an approved drug.