If you have been reading about GHS-R1a and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-05-17. Numbers and descriptions here follow the published literature rather than marketing material.
Ipamorelin is a synthetic pentapeptide classified as a growth hormone secretagogue. Its sequence, Aib-His-D-2-Nal-D-Phe-Lys-NH2, combines three non-proteinogenic residues with a C-terminal amide. The N-terminal aminoisobutyric acid unit and the two aromatic D-amino acids distinguish it from peptides assembled only from standard L-amino acids. Its formula is C38H49N9O5, corresponding to an average mass near 711.9 Da. At neutral pH the molecule carries a net positive charge, a property that shapes its behaviour in chromatographic and electrophoretic systems.
The compound was developed at Novo Nordisk during the 1990s as part of a programme seeking secretagogues with improved selectivity. It was described in the peer-reviewed literature in 1998 alongside related pentapeptides from the same series. Investigators advanced it because it raised growth hormone output in animal models while leaving other pituitary hormones comparatively unaffected. The development code NNC 26-0161 appears in earlier reports, and ipamorelin later became the common designation in published work.
Ipamorelin is a synthetic pentapeptide first described in the 1990s by researchers at Novo Nordisk during a program to develop selective growth hormone secretagogues. Its sequence is Aib-His-D-2-Nal-D-Phe-Lys-NH2, incorporating two non-natural residues, alpha-aminoisobutyric acid and D-2-naphthylalanine. The C-terminus is amidated, and the material is supplied as a white lyophilized powder. The molecular formula is C38H49N9O5 and the monoisotopic mass is approximately 711.85 daltons. The short chain and modified residues give it greater resistance to enzymatic degradation than many larger peptide hormones.
At the molecular level, ipamorelin acts as an agonist at the growth hormone secretagogue receptor type 1a, the same G protein-coupled receptor that binds ghrelin. Receptor activation couples to Gq/11 signaling, raising intracellular calcium through inositol trisphosphate and diacylglycerol, which in turn promotes exocytosis of growth hormone from pituitary somatotroph cells. Ipamorelin binds this receptor with high affinity and shows weak activity at other secretagogue-related targets in vitro. Its action requires the intact receptor and is not reversed by growth hormone-releasing hormone antagonists.
Compared with earlier growth hormone secretagogues such as GHRP-6 and hexarelin, ipamorelin has been reported to produce less stimulation of adrenocorticotropic hormone, cortisol, and prolactin in animal and early human studies. This selectivity is usually attributed to differences in receptor subtype interactions and to the tissue distribution of the receptor. Effects on appetite appear weaker than those of ghrelin itself, although the supporting evidence base is small. Whether these differences produce a distinct clinical profile remains an open question, since controlled human trials are limited.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H49N9O5 | Pentapeptide with C-terminal amide |
| Average mass | Approximately 711.9 Da | Value derived from the formula |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility | Soluble in water and aqueous acetonitrile | Dissolution aided by acidic diluents |
| Common synonyms | Ipamorelin; NNC 26-0161 | Code name used in early reports |
Peptides such as ipamorelin are subject to chemical and physical degradation. Hydrolysis of peptide bonds, oxidation of susceptible residues, and aggregation are common pathways that reduce purity over time. The rate of these processes depends on temperature, moisture, pH, and the number of freeze-thaw cycles a sample undergoes. Because the compound is typically handled as a lyophilized powder, controlling moisture during storage is a central concern. Degradation products can be detected with separation techniques that resolve the parent peptide from related impurities.
Lyophilized material is generally stored frozen and protected from light and moisture. Typical recommendations place dry powder at temperatures well below freezing, while reconstituted solutions are kept cold and used within a defined window. Repeated freezing and thawing should be avoided because it can promote aggregation and loss of material. The choice of solvent matters as well; compatibility with the intended diluent should be checked before preparation. These handling practices aim to preserve both the quantity and the integrity of the peptide.
Research quantities of ipamorelin are typically distributed as a white to off-white lyophilized powder. The solid dissolves readily in water and in aqueous buffers, and stock solutions are commonly prepared in sterile water or a mildly acidic diluent. Adsorption to plastic and glass surfaces can reduce the concentration of very dilute solutions, so containers and transfer steps deserve attention when accurate concentrations matter. Reconstituted material is generally used promptly rather than held for extended periods.
Storage recommendations for the dry solid center on low temperature and low moisture, most often -20 °C in a sealed, desiccated container protected from light. Solutions are less stable than the powder and are usually kept cold and used within a short window. Freeze-thaw cycling is a recognized source of loss, and aliquoting before freezing is a standard precaution. These practices derive from general peptide handling principles rather than from a single published stability trial, so exact shelf lives should be treated as approximate.
Ipamorelin is a synthetic pentapeptide that belongs to the growth hormone secretagogue family. Its sequence is Aib-His-D-2-Nal-D-Phe-Lys-NH2, incorporating two non-natural residues that resist enzymatic breakdown. Researchers at Novo Nordisk described the compound in the 1990s while searching for agents that release growth hormone with fewer side effects than earlier secretagogues. The molecule acts as an agonist at the ghrelin receptor, also called GHS-R1a, which is expressed in the pituitary and in several peripheral tissues.
Selectivity distinguishes ipamorelin from first-generation secretagogues such as GHRP-6. At doses that reliably raise growth hormone, it shows little stimulation of adrenocorticotropic hormone or cortisol release in animal models, and it does not markedly raise prolactin or appetite. Binding at GHS-R1a on pituitary somatotrophs triggers calcium influx and pulsatile growth hormone secretion. Because the compound mimics the natural ghrelin signal, the release pattern tends to follow the body's own rhythm rather than producing a sustained elevation.
Lyophilized material is generally stored cold and dry, with desiccant, and protected from light. In solution the peptide is more vulnerable: the histidine side chain can oxidize, and repeated freeze-thaw cycles promote aggregation and loss of material to container surfaces. A mildly acidic aqueous buffer is often used for short-term handling because it limits several degradation routes. Accurate prediction of long-term stability under a given set of conditions is difficult, and published stability data remain sparse.
Published discussion of this compound is uneven. Some references describe it as a tool for probing growth hormone regulation, while others focus on analytical characterization or on comparisons with related secretagogues. Statements about selectivity, half-life and potency often trace back to a small number of original reports that later authors cite secondhand. Readers evaluating a claim should therefore check whether a figure reflects a direct measurement or a repeated citation, and whether the underlying study was conducted in animals, in isolated cells or in human volunteers.
Macimorelin (INN) – or Macrilen (trade name) – is a drug that was developed by Aeterna Zentaris for use in the diagnosis of adult growth hormone deficiency. Macimorelin acetate, the salt formulation, is a synthetic growth hormone secretagogue receptor agonist. It is a growth hormone secretagogue receptor (ghrelin receptor) agonist, causing release of growth hormone from the pituitary gland. Macimorelin acetate is described chemically as D-Tryptophanamide, 2-methylalanyl-N-[(1R)-1-(formylamino)-2-(1H-indol-3-yl)ethyl]-acetate. Macimorelin (Macrilen) was invented and first synthesized at University of Montpellier, Centre National de la Recherche Scientitifique (CNRS), France. This transpired from a long-lasting research collaboration with Aeterna Zentaris. Aeterna Zentaris later in-licensed macimorelin as a development candidate from the CNRS and proceeded with the pre-clinical and clinical development of the compound. As of January 2014, it was in Phase III clinical trials. The phase III trial for growth hormone deficiency is expected to be complete in December 2016. As of December 2017, it was FDA-approved as a method to diagnose growth hormone deficiency. Traditionally, growth hormone deficiency was diagnosed via means of insulin tolerance test (IST) or glucagon stimulation test (GST). These two means are done parenterally, whereas Macrilen boasts an oral formulation for ease of administration for patients and providers. In November 2018 Novo Nordisk would acquire the rights to Macrilen, at a cost of $145 million.
Hox genes A subset of highly conserved homeobox-containing genes whose protein products function as transcription factors essential for the proper organization of the body plan in developing animal embryos, ensuring that the correct structures are formed in the correct places. Hox genes are usually arranged on a chromosome in tandem arrays and are expressed sequentially during development, with the sequence of gene activation corresponding to their physical arrangement within the genome and/or the physical layout of the tissues in which they are expressed along the organism's anterior–posterior axis.
== Regulatory harmonization == In an effort to reduce the burden on manufacturers applying for orphan drug status, the FDA and the European Medicines Agency (EMA) agreed in late 2007 to utilize a common application process for both agencies. However, the two agencies will continue to maintain separate approval processes.
Sources: en.wikipedia.org
DASH diet The Dietary Approaches to Stop Hypertension (DASH) diet focuses on increasing the consumption of fruits, vegetables, whole grains and low-fat dairy products. DASH offers an intervention to manage elevated blood pressure and to prevent cardiovascular disease non-pharmacologically. Combining the DASH diet with a reduced sodium intake will further decrease blood pressure, but is not required for therapeutic effect. Indeed, it is effective at a wide range of sodium intake levels. More recent reviews of DASH have continued to advocate its efficacy as an affordable weight loss tool, but stress that diet adherence is key to produce the desired results.
Spinal cord The part of the central nervous system housed within the vertebral column. It transmits signals between the brain and the rest of the body and controls reflexes. Split-brain A condition resulting from surgical severing of the corpus callosum, often performed to treat severe epilepsy. Reveals the functional specialization of brain hemispheres. Stellate cell A star-shaped neuron, often GABA-ergic, found in regions like the cerebellum and somatosensory cortex. Stiles–Crawford effect A phenomenon in visual perception where light rays entering the eye near the center of the pupil are more effective in eliciting a visual response than those entering near the edge. Striatum A major component of the basal ganglia, involved in movement, reward, and procedural learning. Composed of the caudate nucleus and putamen. Stroke A condition where poor blood flow to the brain results in cell death. Symptoms depend on the affected brain region and may include paralysis, speech impairment, and memory loss. Subarachnoid space The area between the arachnoid mater and the pia mater, filled with cerebrospinal fluid that cushions the brain and spinal cord. Substantia nigra A midbrain structure involved in movement and reward. Degeneration of dopaminergic neurons here leads to Parkinson's disease. Sulcus A groove on the surface of the cerebral cortex that separates adjacent gyri. Prominent sulci define major brain lobes and landmarks. Superior colliculus A structure in the midbrain involved in visual processing and control of eye movements. Part of the tectum.
If it is impossible to say the sound without fogging a nasal mirror, there is an air leak, reasonable evidence of poor palatal closure. Speech is often unclear due to the inability to pronounce certain sounds. One of the surgical treatments for velopalatal insufficiency involves tailoring the tissue from the back of the throat and using it to purposefully cause partial obstruction of the opening of the nasopharynx. This may actually cause OSA syndrome in susceptible individuals, particularly in the days following surgery, when swelling occurs (see below: Special Situation: Anesthesia and surgery). Finally, patients with OSA are at an increased risk of many perioperative complications when they are present for surgery, even if the planned procedure is not on the head and neck. Guidelines to reduce the risk of perioperative complications have been published.
Sources: en.wikipedia.org
A.R.T.I.: a lighthearted voxel-based game that allowed for open-ended creation and destruction in a vein similar to Minecraft. It was resurrected as a VR game but shelved again when Half-Life: Alyx eclipsed its development. SimTrek: a virtual reality game developed primarily by the creators of Kerbal Space Program. It was cancelled during the development of Half-Life: Alyx. In the Valley of Gods: a period adventure game set in 1920s Egypt developed by Campo Santo, a studio acquired by Valve in 2018. It was put on hold in late 2019, with the designers shifting to other Valve projects.
A study found comparable absorption of transdermal estradiol patches (within ±25% of reference) for a number of skin sites including the abdomen, upper arm, upper thigh, lower back, and side. However, absorption was 15% lower for the upper thigh compared to the abdomen and the difference was significant. Another study found that transdermal estradiol patches had 20 to 25% higher bioavailability when applied to the buttocks than when applied to the abdomen. Studies of topical steroids have found that the scrotum is especially permeable among skin sites. Studies of transdermal testosterone cream, gel, and patches applied to the scrotum in men have observed 5- to 8-fold higher levels of testosterone than with application to conventional skin sites. In a study of topical application of hydrocortisone solution in men, skin permeability (defined as total radiolabeled urinary excretion) relative to the forearm (1.0) was 42.0 for the scrotum, 13.0 for the jaw angle, 6.0 for the forehead, 3.6 for the underarm, 3.5 for the scalp, 1.7 for the back, 0.8 for the palm of the hand, 0.4 for the ankle, and 0.1 for the sole of the foot. In accordance with findings with other topical steroids, a study in men with prostate cancer treated with transdermal estradiol patches applied to the scrotum observed about 5-fold higher estradiol levels relative to application to conventional skin sites such as the forearm. Penile skin may have similarly enhanced absorption characteristics relative to scrotal skin.
The clinical relevance of the results published by Auchus in 2004 was demonstrated in 2012 for the first time when Kamrath et al. attributed the urinary metabolites to the androgen backdoor pathway from 17OHP to DHT in patients with steroid 21-hydroxylase (encoded by the gene CYP21A2) enzyme deficiency. Barnard et al. in 2017 demonstrated metabolic pathways from C21 steroids to 11KDHT that bypasses A4 and T, an aspect that is similar to that of the backdoor pathway to DHT. These newly discovered pathways to 11-oxygenated androgens were also described as "backdoor" pathways due to this similarity, and were further characterized in subsequent studies.
Sources: en.wikipedia.org
It is a synthetic five-amino-acid peptide that acts as a growth hormone secretagogue. Three of its residues are non-standard amino acids, and the chain ends in an amide rather than a free acid. The molecule is small enough that it can be characterised by routine peptide analytical techniques.
It has not received marketing approval as a medicine in the United States or the European Union. Supplied material is generally described and handled as a research chemical. Regulatory treatment varies by jurisdiction, and some countries restrict growth hormone secretagogues under sports or medicines legislation.
Earlier secretagogues were associated with broader hormonal responses, including measurable changes in cortisol and prolactin. Reports on this peptide describe a narrower profile in which growth hormone release is the most prominent effect. The observation is influential because it shapes how the compound is compared with other members of the same receptor family.
It is a synthetic pentapeptide belonging to the growth hormone secretagogue family. Its principal characterized target is the ghrelin receptor, also called GHS-R1a. The molecule contains non-natural amino acids and an amidated C-terminus.