Ipamorelin

Ipamorelin (development code NNC 26-0161) is a synthetic pentapeptide growth hormone secretagogue composed of five amino acids in the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2 ⁽¹⁾. It was developed in the late 1990s by Novo Nordisk in Denmark as a third-generation improvement on earlier GHRP compounds, derived from GHRP-1 by removing the central dipeptide Ala-Trp ^(1,5). The result was a compound that retained the full GH-releasing potency of its predecessors while eliminating the off-target hormonal effects that limited their utility.

What defines Ipamorelin within the growth hormone secretagogue class is its selectivity. In the landmark 1998 study by Raun et al., published in the European Journal of Endocrinology, Ipamorelin was shown to stimulate GH release without significant increases in ACTH or cortisol, even at doses more than 200-fold above the ED50 for GH release ⁽¹⁾. This made it the first GHRP-receptor agonist with a selectivity profile matching that of GHRH itself. No other GHRP, including GHRP-2, GHRP-6, or Hexarelin, achieves this level of hormonal specificity.

Ipamorelin entered Phase II clinical trials sponsored by Helsinn Therapeutics for the treatment of postoperative ileus (delayed bowel recovery after surgery). Still, these trials were discontinued after the clinical endpoints did not reach statistical significance compared with placebo ^(5,6). It is not FDA-approved for any therapeutic indication and has not been placed on the FDA’s Category 2 list. All Healius Peptides Ipamorelin is sold strictly for in vitro research purposes.

Ipamorelin functions as a selective agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the same receptor targeted by the endogenous hormone ghrelin and by other GHRP-class peptides. GHS-R1a is a G-protein-coupled receptor expressed on somatotroph cells in the anterior pituitary gland, as well as in hypothalamic nuclei and peripheral tissues, including the GI tract, liver, and pancreas ^(1,5).

When Ipamorelin binds GHS-R1a on pituitary somatotrophs, it triggers intracellular signaling cascades involving cyclic adenosine monophosphate (cAMP) production and phospholipase C (PLC) activation. It increases intracellular calcium, which prompts exocytosis of stored GH vesicles ^(1,7). At the hypothalamic level, Ipamorelin stimulates growth hormone-releasing hormone (GHRH) neurons while suppressing somatostatin output, amplifying the pituitary GH pulse ⁽⁷⁾. The resulting GH release is pulsatile, mirroring the body’s natural circadian secretion pattern rather than producing a sustained, non-physiological elevation.

The critical difference between Ipamorelin and other ghrelin receptor agonists lies in what it does not do. Both GHRP-2 and GHRP-6 activate the ACTH-cortisol axis and stimulate prolactin release at GH-effective doses ^(1,8). Ipamorelin produces none of these secondary effects. It also lacks the potent orexigenic (appetite-stimulating) activity characteristic of GHRP-6 ⁽¹⁾. This selectivity is attributed to a receptor-binding profile that preferentially activates the GH pathway, without broad hypothalamic activation of stress or feeding circuits.

Growth Hormone Secretion

In vivo studies in anesthetized rats showed Ipamorelin released GH with potency and efficacy comparable to GHRP-6 (ED50 = 80 nmol/kg vs 115 nmol/kg for GHRP-6) ⁽¹⁾. In conscious swine, Ipamorelin produced GH release with an ED50 of 2.3 nmol/kg and peak GH concentrations of approximately 65 ng/mL ⁽¹⁾. In healthy human subjects, Ipamorelin induced GH release with a peak at approximately 40 minutes post-administration, followed by a rapid decline, consistent with the natural pulsatile pattern ⁽⁵⁾.

Bone Mineral Density and Growth

A 12-week study in adult female rats demonstrated that Ipamorelin dose-dependently increased longitudinal bone growth rate, from 42 micrometers per day in the vehicle group to 52 micrometers per day at the highest dose (P < 0.0001) ⁽²⁾. A separate study by Svensson et al. confirmed that both Ipamorelin and GHRP-6 increased bone mineral content in adult female rats, with Ipamorelin producing these effects without the cortisol and prolactin elevations seen with GHRP-6 ⁽⁹⁾. These findings have positioned Ipamorelin as a research tool for studying GH-mediated bone metabolism and age-related bone loss.

Insulin Secretion

A study by Adeghate and Ponery investigated the mechanism of Ipamorelin-evoked insulin release from pancreatic tissue in both normal and diabetic rat models ⁽³⁾. The researchers found that Ipamorelin significantly increased insulin secretion through calcium-channel-dependent and adrenergic-receptor-mediated pathways. This dual mechanism of action on pancreatic beta cells opens avenues for research in metabolic regulation and glucose homeostasis.

Gastric Motility

Animal model data from Greenwood-Van Meerveld et al. showed that Ipamorelin accelerated gastric emptying in fasted rats with induced post-operative ileus ⁽⁴⁾. Repetitive intravenous administration was associated with increased fecal pellet output, food intake, and body weight gain ⁽⁵⁾. While the Phase II human clinical trial for postoperative ileus did not meet its primary endpoint, the preclinical gastric motility data remain relevant to GI motility research ⁽⁶⁾.

Glucocorticoid-Induced Muscle and Bone Protection

Ipamorelin has been shown to counteract the catabolic effects of glucocorticoids in animal models. In adult rats treated with methylprednisolone, co-administration of Ipamorelin significantly increased muscle strength and improved nitrogen balance compared to glucocorticoid-only controls ⁽¹⁰⁾. These findings suggest potential research applications in catabolic wasting conditions driven by chronic corticosteroid exposure.

Healius Peptides supplies Ipamorelin as a lyophilized powder in sterile, sealed vials in two sizes: 5mg and 10mg. Reconstitution requires bacteriostatic water (BAC water).

Reconstitution

Draw the desired volume of BAC water into a sterile syringe. Insert the needle through the vial stopper and direct the stream slowly down the inside wall of the vial. Do not aim directly at the lyophilized pellet. Allow the powder to dissolve naturally; gently swirl if needed, but do not shake. The resulting solution should be clear and free of particulate matter. Use our Ipamorelin dosage calculator to determine the correct reconstitution volume for your target concentration.

Research Dosage Ranges

In clinical and preclinical literature, Ipamorelin doses typically range from 100 to 300 micrograms per administration via subcutaneous injection ^(1,5). The most commonly referenced protocol calls for 200 to 300 micrograms administered once to three times daily. Bedtime dosing is frequently emphasized (also spelled emphasized) in research protocols, timed to amplify the natural nocturnal GH surge. Ipamorelin has a circulating half-life of approximately 2 hours, which supports multiple daily administrations for sustained pulsatile GH stimulation ⁽⁵⁾.

Storage

Store unreconstituted Ipamorelin at -20°C for long-term stability. Once reconstituted with BAC water, store the vial at 2 to 8°C (standard refrigerator temperature) and use within 14 to 21 days. Avoid repeated freeze-thaw cycles. Protect from direct light.

Ipamorelin has the most favorable safety profile among GHRP-class compounds, a direct consequence of its selectivity. The Raun et al. data showed no significant elevation of ACTH, cortisol, prolactin, FSH, LH, or TSH at any dose tested, including doses 200-fold above the GH-releasing ED50 ⁽¹⁾. Clinical trials in human subjects reported good safety and tolerability with no serious adverse events ^(5,6).

Reported Effects

Mild, transient headache during the first few days of administration is the most commonly reported effect in clinical settings. Occasional lightheadedness or mild flushing shortly after injection has been noted, consistent with the acute GH pulse. Injection site irritation (redness, mild swelling) occurs at rates comparable to any subcutaneous peptide injection ^(5,6).

What Ipamorelin Does Not Do

This is the defining advantage. Ipamorelin does not raise cortisol. It does not raise ACTH. It does not raise prolactin. It does not stimulate appetite ⁽¹⁾. These are the primary side-effect concerns with GHRP-2 and GHRP-6, and Ipamorelin avoids them all. For researchers who need to isolate the effects of GH release from confounding variables such as cortisol, prolactin, or changes in appetite, Ipamorelin is the only GHRP-class option that delivers a genuinely clean signal.

Sermorelin (GRF 1-29) and Ipamorelin are frequently compared because both are considered “clean” GH-releasing compounds with minimal off-target effects. The key difference lies in the receptors they target, and this difference has practical consequences for their performance in research protocols.

Receptor Pathway

Sermorelin is a GHRH analog that binds the GHRH receptor on pituitary somatotrophs. Ipamorelin is a ghrelin mimetic that binds GHS-R1a. These are two entirely separate receptor systems that converge on the same GH-releasing cellular machinery through different intracellular signaling cascades ^(1,7). This distinction is why the two compounds synergize so effectively when co-administered: Sermorelin increases the number of somatotrophs releasing GH. In contrast, Ipamorelin increases the amount of GH released per somatotroph ⁽⁷⁾.

GH Selectivity

Both compounds are GH-selective. Sermorelin and Ipamorelin do not elevate cortisol, ACTH, or prolactin ⁽¹⁾. On this metric, they are functionally equivalent. The practical differences lie in potency (Ipamorelin produces larger peak GH responses than Sermorelin at matched doses) ^(1,8) and in regulatory history (Sermorelin achieved FDA approval as Geref in 1997 before being voluntarily withdrawn for commercial reasons).

Half-Life and Dosing

Sermorelin has a very short circulating half-life (approximately 10 to 20 minutes), requiring precise timing of administration. Ipamorelin has a longer half-life of approximately 2 hours, providing a wider dosing window and more sustained GH pulse amplitude ⁽⁵⁾. For protocols requiring flexibility in administration timing, Ipamorelin is the simpler option.

Tesamorelin is a GHRH analog (like Sermorelin) with a key distinction: it is FDA-approved (as Egrifta/Egrifta SV) for the treatment of HIV-associated lipodystrophy, giving it the strongest regulatory pedigree among GH secretagogues currently in clinical use. Comparing it to Ipamorelin means comparing the two cleanest compounds from each side of the GH axis: the best GHRH analog versus the best GHRP.

Receptor and Pathway

Tesamorelin targets the GHRH receptor. Ipamorelin targets GHS-R1a. As with Sermorelin, these different pathways make the two compounds complementary rather than directly competitive ⁽⁷⁾. The Tesamorelin + Ipamorelin combination has become a research topic in its own right, with combined query volume reflecting strong interest in the pairing.

Clinical Evidence

Tesamorelin has the edge on clinical data. Its FDA-approved status means it has undergone Phase III trials with published safety and efficacy data in human subjects. Ipamorelin’s clinical trial history is limited to the discontinued Phase II post-operative ileus studies ^(5,6). For research protocols in which regulatory precedent or published human safety data are priorities, Tesamorelin carries greater weight. For protocols requiring GH release via the GHRP pathway (e.g., ghrelin receptor pharmacology, GHS-R1a signaling studies), Ipamorelin is the necessary compound.

Lipolytic Profile

Tesamorelin has demonstrated specific visceral fat reduction in clinical trials, a property that appears to go beyond its GH-releasing effect alone ⁽¹¹⁾. Ipamorelin’s effects on body composition are mediated entirely through GH and downstream IGF-1, without a direct lipolytic mechanism independent of the GH axis. Researchers specifically interested in visceral adiposity models may find Tesamorelin more directly applicable.

1. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin is the first selective growth hormone secretagogue. European Journal of Endocrinology. 1998;139(5):552-561. Novo Nordisk developed Ipamorelin pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2). GH potency comparable to GHRP-6. No ACTH or cortisol elevation at 200x ED50. First GHRP-receptor agonist with GHRH-like selectivity. Swine data: ED50 2.3 nmol/kg, Emax 65 ng GH/mL. GHRP-2 has higher potency (ED50 0.6 nmol/kg) but lower selectivity.

2. Johansen PB, Nowak J, Skjaerbaek C, et al. Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats. Growth Hormone and IGF Research. 1999;9(2):106-113. Novo Nordisk study. Adult female rats, 15-day ipamorelin s.c. three times daily. Dose-dependent increase in longitudinal bone growth rate: 42 to 52 micrometers/day (P < 0.0001). Pronounced dose-dependent body weight gain.

3. Adeghate E, Ponery AS. Mechanism of ipamorelin-evoked insulin release from the pancreas of normal and diabetic rats. Neuroendocrinology Letters. 2004;25(6):403-406. Ipamorelin increased insulin secretion through calcium channel-dependent and adrenergic receptor-mediated pathways in both healthy and diabetic rat pancreatic tissue.

4. Greenwood-Van Meerveld B, et al. Ipamorelin accelerates gastric emptying in fasted adult male rats with induced post-operative ileus. Preclinical gastric motility data showing increased fecal pellet output, food intake, and body weight gain with repetitive ipamorelin administration.

5. Ishida J, Saitoh M, Ebner N, et al. Growth hormone secretagogues: history, mechanism of action, and clinical development. JCSM Rapid Communications. 2020;3(1):25-37. Review of ipamorelin development by Novo Nordisk (NNC 26-0161). GH peak at 0.67h post-administration in healthy subjects. Phase II trials for post-operative ileus (Helsinn Therapeutics). Tabimorelin is derived from ipamorelin.

6. Beck DE, Sweeney WB, McCarter MD, and Ipamorelin 201 Study Group. Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. International Journal of Colorectal Disease. 2014. Clinical endpoints did not reach statistical significance vs placebo.

7. Growth hormone secretagogue synergy reference. GHRH and GHRP pathways converge on pituitary somatotrophs via distinct intracellular signaling cascades. GHRH increases the number of somatotrophs releasing GH; GHRPs increase GH output per somatotroph. Ipamorelin suppresses somatostatin. Combined GH output exceeds the sum of individual effects.

8. Arvat E, Di Vito L, Maccagno B, et al. Effects of GHRP-2 and Hexarelin on GH, prolactin, ACTH, and cortisol levels in man. Peptides. 1997;18(6):885-891. GHRP-2 and Hexarelin both elevate ACTH and cortisol (comparable to hCRH). GHRP-6 similarly elevates cortisol. Comparison benchmark for Ipamorelin’s clean selectivity profile.

9. Svensson J, Lall S, Dickson SL, et al. The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats. Journal of Endocrinology. 2000;165(3):569-577. 12-week treatment. Ipamorelin increased bone mineral content without elevating cortisol or prolactin, unlike GHRP-6.

10. Aagaard NK, Grofte T, Greisen J, et al. Effects of growth hormone and growth hormone secretagogues on nitrogen balance and urea synthesis in steroid-treated rats. Growth Hormone and IGF Research. 2009;19(5):426-431. Ipamorelin counteracted glucocorticoid-induced catabolic effects. Improved muscle strength and nitrogen balance with methylprednisolone co-administration.

11. Tesamorelin clinical data. FDA-approved as Egrifta/Egrifta SV (2010) for HIV-associated lipodystrophy. Demonstrated specific visceral fat reduction in Phase III trials beyond the GH-releasing effect alone. Regulatory and clinical evidence benchmark for GHRH-class compounds.

This product is intended for laboratory research use only. It is not a drug, food, cosmetic, or dietary supplement, and it is not intended for human or veterinary consumption. The U.S. Food and Drug Administration has not approved Ipamorelin for any therapeutic indication. All information provided in this document is drawn from published, peer-reviewed scientific literature and is intended solely to support researchers in designing and interpreting in vitro studies. Healius Peptides makes no claims regarding the safety, efficacy, or suitability of this product for any use other than laboratory research. Buyers accept full responsibility for ensuring their use complies with all applicable local, state, federal, and international regulations.