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Ipamorelin

Growth Hormone

Selective GHRP / ghrelin receptor agonist

Ipamorelin is a synthetic pentapeptide that stimulates the release of growth hormone (GH) by mimicking the action of ghrelin.

§Dosing at a glance

2 protocols · from the research
What it's forDoseHow oftenHowFor how long
Human Clinical Studies0.03 mg/kgTwice daily——
Animal Studies (preclinical reference ranges)18–450 mcg/day3× dailySubcutaneousInjected just under the skin, into the fat layer.3 mos

Approximate values pulled from the research — double-check before dosing.

§01Summary

Ipamorelin is a synthetic pentapeptide that stimulates the release of growth hormone (GH) by mimicking the action of ghrelin, a naturally occurring appetite and metabolism hormone. Unlike earlier growth hormone-releasing peptides, ipamorelin appears to selectively trigger GH secretion without significantly elevating stress hormones such as cortisol or ACTH, even at high doses5. This selectivity has made it a focus of research in areas ranging from surgical recovery to bone health and muscle preservation.

In animal models, ipamorelin has been reported to increase longitudinal bone growth8, counteract the muscle and bone loss associated with corticosteroid use19, and improve gastrointestinal motility following abdominal surgery11. In a human clinical trial involving patients recovering from bowel resection, ipamorelin may shorten the time to tolerating a solid meal after surgery1, though the full picture of its clinical utility continues to emerge across multiple registered trials. Its pharmacokinetics in humans are well characterized, with a short half-life of approximately two hours and predictable, dose-dependent GH stimulation2, supporting a foundation for ongoing clinical development across several therapeutic areas.

This is the layperson summary. Mechanism, dosing, the evidence base, and the published literature are in the sections below — every claim links to its source.

§02In depth

Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) that acts as a selective agonist at the growth hormone secretagogue receptor type 1a (GHSR1a), the endogenous receptor for ghrelin5. Upon binding GHSR1a on pituitary somatotroph cells, ipamorelin activates Gq/11-coupled intracellular signaling, increasing intracellular calcium and stimulating episodic GH release in a concentration-dependent manner2,5. Its in vitro EC50 at the rat pituitary is approximately 1.3 nmol/L, with in vivo ED50 values of 80 nmol/kg (rats) and 2.3 nmol/kg (swine) for GH release5.

Ipamorelin's defining pharmacological characteristic is its exceptional hormonal selectivity. Unlike GHRP-6 and GHRP-2, which stimulate ACTH and cortisol release through additional receptor interactions, ipamorelin produces no significant elevation of ACTH, cortisol, FSH, LH, prolactin, or TSH even at doses more than 200-fold above the GH-releasing ED505. This selectivity profile more closely resembles endogenous GHRH than other GHSR1a agonists, establishing ipamorelin as the first member of this class with such specificity5. Mechanistic evidence also suggests that GHRPs including ipamorelin may partly act by stimulating endogenous ghrelin secretion from glandular stomach tissue, contributing to GH release via an indirect route16.

Downstream of GH release, ipamorelin drives classic GH-axis anabolic and metabolic effects: it promotes longitudinal bone growth and increases periosteal bone formation through mechanisms that appear independent of changes in circulating IGF-I8, improves nitrogen balance and reduces hepatic urea synthesis capacity under catabolic conditions18, and counteracts glucocorticoid-induced suppression of muscle tetanic tension and bone formation19. Chronic administration produces somatotroph priming — increasing secretory granule density and sensitizing the pituitary to subsequent stimulation by heterologous secretagogues — through a mechanism distinct from GHRH-mediated sensitization15.

In the gastrointestinal system, ipamorelin acts through peripheral GHSR1a to restore cholinergic neuromuscular transmission in surgically inhibited gastric smooth muscle, accelerating gastric emptying and colonic transit9,11. It also attenuates visceral hypersensitivity and somatic allodynia via peripheral ghrelin receptor pathways without requiring central nervous system penetration14, in contrast to the central mechanisms required for its anti-emetic effects10.

Human pharmacokinetics are characterized by dose-proportional linear kinetics, a terminal half-life of approximately 2 hours, plasma clearance of 0.078 L/h/kg, and volume of distribution of 0.22 L/kg2. Elimination is predominantly urinary — a distinctive feature compared to other GHRPs that are cleared primarily via biliary excretion — and 60–80% of administered dose is recoverable as intact peptide17. Intranasal bioavailability is approximately 20% in rats17, and oral bioavailability in dogs supports measurable GH elevation after oral dosing12. Inter-individual variability in pharmacodynamic GH response is substantially greater than in pharmacokinetic parameters, suggesting that somatotroph responsiveness is a key variable in clinical dosing optimization2.

§04Evidence & efficacy

Evidence base
69Studies
11Human
19Animal

Ipamorelin's most thoroughly investigated clinical application is the management of postoperative ileus following bowel resection. In a prospective, randomized, controlled proof-of-concept trial, ipamorelin may shorten the median time to first tolerated meal after surgery (25.3 hours versus 32.6 hours for placebo)1, representing a clinically meaningful numerical trend. Phase II dose-finding trials in GI recovery following bowel resection are registered and in active development3,4.

In animal models, ipamorelin produces well-replicated, dose-dependent GH release across rat and swine species5, and has been reported to increase longitudinal bone growth8, expand bone mineral content through increased bone dimensions7, counteract glucocorticoid-induced losses in bone formation and muscle strength19, improve nitrogen balance under steroid-induced catabolic conditions18, and accelerate gastric emptying in postoperative ileus models9,11. Repetitive dosing in rodent POI models improved cumulative fecal output, food intake, and body weight recovery beyond the effects of single dosing11. Ipamorelin has also been reported to attenuate visceral and somatic pain in rodent models via peripheral ghrelin receptor activation14, and to reduce cisplatin-associated weight loss in ferrets10, suggesting potential utility in chemotherapy supportive care. Human pharmacokinetic-pharmacodynamic modeling confirms dose-proportional, concentration-dependent GH stimulation in volunteers2.

§05Safety

Ipamorelin has demonstrated a favorable tolerability profile across available human and animal data. In the largest human trial to date, overall treatment-emergent adverse events were numerically lower in the ipamorelin group (87.5%) compared to placebo (94.8%) in 114 surgical patients, and no serious adverse events were attributed to ipamorelin1. Human pharmacokinetic studies did not report significant adverse events across a broad range of IV doses2.

In animal models, ipamorelin's most distinctive safety feature is its selectivity: it does not significantly elevate ACTH or cortisol even at doses exceeding 200-fold the GH ED50, and has no observed effect on FSH, LH, prolactin, or TSH5. This hormonal selectivity compares favorably to related peptides such as GHRP-6 and GHRP-2, which do stimulate ACTH and cortisol release5. Chronic pituitary studies in rats showed no gross morphological changes to somatotroph cells and only mild, receptor-specific desensitization to repeated ipamorelin challenge, with preserved responsiveness to GHRH8,15.

One metabolic observation from animal studies is that ipamorelin, like other GH secretagogues, may increase body fat and food intake via GH-independent mechanisms, with elevated leptin observed in treated animals6. This orexigenic and adipogenic signal, distinct from the expected anabolic GH-related effects, is an active area of characterization. Neither hepatotoxicity nor renal toxicity signals have been reported in available studies. Long-term human safety data are being established through ongoing clinical investigations3,4.

§06History

Ipamorelin was developed by Novo Nordisk in the late 1990s as part of a systematic effort to identify novel growth hormone secretagogues with improved selectivity over earlier GH-releasing peptides such as GHRP-2 and GHRP-6. The foundational characterization of its pharmacology was published in 1998, demonstrating for the first time that a GHSR1a agonist could stimulate GH release with potency comparable to GHRP-6 while displaying a hormonal selectivity profile — absent effects on ACTH, cortisol, and other pituitary hormones — that had previously been associated only with endogenous GHRH5. Concurrent medicinal chemistry work at Novo Nordisk explored ipamorelin-derived peptidomimetics in pursuit of orally bioavailable analogs, establishing early evidence that ipamorelin itself possesses measurable oral activity in dogs12. Detailed pharmacokinetic studies in rats characterized its distinctive urinary excretion profile and nasal bioavailability17.

Clinical development was subsequently pursued by Helsinn Therapeutics, which advanced ipamorelin into Phase II trials for postoperative ileus and GI recovery following bowel resection, with multiple trials registered in the 2008–2011 period3,4. A prospective, randomized proof-of-concept trial in 114 bowel resection patients was published in 2014, providing the first peer-reviewed human efficacy and safety data for this indication1. Human pharmacokinetic-pharmacodynamic modeling was formally published in 1999, establishing the quantitative basis for clinical dose selection2. Preclinical research has continued to expand the understanding of ipamorelin's biological activities, with investigations into pain modulation14, chemotherapy-related weight loss10, and reproductive endocrinology20 published through 2024, reflecting ongoing scientific interest across multiple therapeutic domains.

§07References