Ipamorelin
A selective growth hormone secretagogue with real human pharmacology data — and a Phase 3 programme for postoperative ileus that did not meet its endpoints
🧑🐀 Both
- Also known as
- NNC 26-0161
- Class
- Synthetic pentapeptide, selective GHS-R1a (ghrelin receptor) agonist
- Sequence
- Aib-His-D-2-Nal-D-Phe-Lys-NH₂
- Molecular weight
- ~711.85 g/mol
- CAS number
- 170851-70-4
- Developed by
- Novo Nordisk A/S, mid-1990s (Raun et al.)
- Clinical development
- Helsinn Therapeutics pursued Phase 2/3 trials for postoperative ileus (~2007–2011); programme terminated after trials did not meet primary endpoints.
- Regulatory status
- Not approved for human use anywhere. No active IND/NDA on record as of 2026.
What it is
Ipamorelin is a synthetic pentapeptide developed at Novo Nordisk in the mid-1990s and first described by Raun and colleagues in 1998. It binds and activates the growth hormone secretagogue receptor (GHS-R1a), triggering acute GH pulses from pituitary somatotrophs. What distinguished it at discovery was selectivity: earlier secretagogues — GHRP-6 and GHRP-2 — also released cortisol, ACTH, and prolactin. Ipamorelin was the first GHS shown to release GH without meaningfully activating those parallel axes.
The most developed clinical indication was postoperative ileus (POI) — transient bowel-function paralysis following abdominal surgery. Because GHS-R1a is expressed in gastrointestinal smooth muscle, ipamorelin was hypothesised to accelerate bowel-motility recovery. Helsinn Therapeutics ran Phase 2 and Phase 3 trials. The Phase 3 programme did not meet primary endpoints and was terminated. Ipamorelin has not been approved for any use.
How it works
Ipamorelin binds GHS-R1a in the pituitary and hypothalamus. Receptor activation raises intracellular calcium via Gq-coupled signalling, triggering somatotrophs to release a GH pulse. Crucially, somatostatin-mediated feedback remains intact, so ipamorelin produces pulsatile GH rather than sustained elevation — a more physiological pattern than continuous infusion. The selectivity for GHS-R1a over pathways that drive ACTH and prolactin release is encoded by the non-natural amino acids in the sequence, particularly D-2-naphthylalanine at position 3 and the C-terminal amide. This distinguishes it from GHRP-6 and GHRP-2, which activate those parallel axes at pharmacological doses.
Downstream, GH pulses drive hepatic IGF-1 production and acutely stimulate anabolic signalling in bone and muscle. GHS-R1a is also expressed in gastrointestinal smooth muscle, and receptor activation there promotes prokinetic contractions — the rationale behind the postoperative ileus programme.
What the research shows
The ipamorelin literature falls into three categories: the original pharmacology and PK/PD work from Novo Nordisk, rodent studies on bone and body composition, and the clinical programme for postoperative ileus. The human evidence base is real but limited — Phase 2 and Phase 3 trials were conducted, but the Phase 3 did not demonstrate efficacy for the primary endpoint, and no further clinical development has followed.
Raun et al. (1998) — Discovery: the first selective GH secretagogue
Raun K. et al., 1998, European Journal of Endocrinology, 139(5):552–561 🧑🐀 Both (in vitro, animal, and human pituitary data)
The foundational Novo Nordisk discovery paper. Raun and colleagues characterised ipamorelin's receptor affinity, in vitro GH release from rat pituitary cells, and in vivo GH release in pigs and rats versus GHRP-6 and GHRH, with human pituitary cell data also reported.
Ipamorelin was equipotent to GHRP-6 for GH release but, unlike GHRP-6, did not raise cortisol, ACTH, or prolactin at any tested dose — establishing it as the first GHS with a genuinely selective profile.
Limitations: Discovery-stage paper; primary readout is acute GH release, not downstream efficacy or long-term safety. Cortisol/ACTH selectivity was demonstrated in animal and in vitro systems.
Gobburu et al. (1999) — PK/PD modelling in humans
Gobburu J.V.S. et al., 1999, Journal of Pharmacology and Experimental Therapeutics, 291(1):245–252 🧑 Human (PK/PD modelling)
A nonlinear mixed-effects PK/PD modelling study in human volunteers that linked plasma ipamorelin concentrations to the GH secretory response, characterising Emax, EC50, and the time course of GH pulses. The model confirmed pulsatile GH release governed by somatostatin-dependent feedback, consistent with normal physiological regulation. The data established the quantitative exposure–response relationship in humans and supported dose selection for later clinical trials.
Limitations: Primary endpoint is the GH response, not any downstream clinical outcome. This does not establish therapeutic efficacy for any indication.
Beck et al. (2014) — Phase 2 proof-of-concept trial in postoperative ileus
Beck D.E. et al., 2014, Diseases of the Colon & Rectum, 57(12):1403–1411 🧑 Human (Phase 2 RCT)
A multicentre, double-blind, placebo-controlled Phase 2 proof-of-concept trial in adults undergoing small or large bowel resection by open or laparoscopic surgery. One hundred fourteen patients received intravenous ipamorelin 0.03 mg/kg or placebo twice daily from postoperative day 1 to day 7 or hospital discharge. Primary endpoints assessed return-of-bowel-function milestones: time to first flatus, first bowel movement, and tolerance of solid food.
Ipamorelin was well tolerated. No significant differences were observed between ipamorelin and placebo on any primary or secondary efficacy endpoint. The bowel-function recovery timeline was similar across arms. The trial did not provide evidence that ipamorelin accelerates return of bowel function after abdominal surgery at the studied dose.
Limitations: Negative proof-of-concept result. A subsequent Phase 3 programme was conducted but also did not meet primary endpoints; those results have not been published in peer-reviewed form. The failure may reflect dosing, the specific population, or genuine absence of clinically meaningful GI prokinetic effect in the postoperative context.
Johansen et al. (1999) — Longitudinal bone growth in rats
Johansen P.B. et al., 1999, Growth Hormone & IGF Research, 9(2):106–113 🐀 Animal (rats)
Adult female rats received subcutaneous ipamorelin three times daily at 0, 18, 90, or 450 µg/day for 15 days. Longitudinal bone growth was measured by intravital tetracycline fluorescence labelling of the proximal tibial metaphysis. Body weight, serum IGF-1, and IGF binding proteins were also tracked.
Ipamorelin dose-dependently increased longitudinal growth rate from 42 to 52 µm/day, with significant body weight gain. The effect occurred without a corresponding rise in serum IGF-1 or bone turnover markers, suggesting a direct GH-mediated local skeletal effect rather than a purely IGF-1-driven one.
Limitations: Rat study; three-times-daily dosing is not clinically standard. Effects on bone growth in healthy adult humans have not been studied in RCTs.
Svensson et al. (2000) — Bone mineral content in rats (ipamorelin vs GHRP-6)
Svensson J. et al., 2000, European Journal of Endocrinology, 142(1):78–84 🐀 Animal (rats)
Adult female rats were treated for 12 weeks with ipamorelin or GHRP-6 and bone mineral content (BMC) was measured by dual-energy X-ray absorptiometry (DXA) at the femur and lumbar spine. Both peptides significantly increased BMC relative to vehicle controls, with ipamorelin and GHRP-6 producing comparable effects.
Both peptides significantly increased BMC versus vehicle, extending the time horizon of the Johansen bone growth findings to 12 weeks of chronic treatment. Prolactin and cortisol remained unaffected, consistent with ipamorelin's selectivity profile.
Limitations: Rat model; adult rodent bone remodelling does not replicate human dynamics. No fracture-risk or functional bone-quality data in humans.
Andersen et al. (2001) — Ipamorelin counters glucocorticoid-induced bone loss in rats
Andersen N.B. et al., 2001, European Journal of Endocrinology, 144(5):541–546 🐀 Animal (rats)
Rats were treated with prednisolone to induce glucocorticoid-mediated suppression of bone formation and then co-administered ipamorelin. Periosteal bone formation rate, serum osteocalcin, and maximal tetanic muscle tension were assessed at the end of the treatment period.
Periosteal bone formation rate increased four-fold in the prednisolone-plus-ipamorelin group versus prednisolone alone, and maximal muscle tension was partially restored. The data raise the hypothesis of a protective role in glucocorticoid-related osteoporosis, though this has not been pursued clinically.
Limitations: Rat model only; steroid-induced bone suppression differs mechanistically in humans. No clinical trials in glucocorticoid-treated patients have been conducted.
Reported benefits (from research)
- Ipamorelin reliably stimulated GH secretion in a dose-dependent manner in both animal and human pharmacology studies, with a selectivity profile that did not elevate cortisol, prolactin, or ACTH at effective GH-releasing doses — a key pharmacological advantage over earlier GHSs (Raun et al., 1998).
- In healthy volunteers, single IV doses of 10 µg/kg ipamorelin produced GH pulses comparable in amplitude to those seen with GHRP-6, confirming translation of the rat pharmacology to humans (Gobburu et al., 1999).
- In rat models of glucocorticoid-induced bone loss, ipamorelin increased bone mineral content and cross-sectional bone area compared with controls, suggesting a GH-dependent anabolic effect on bone (Svensson et al., 2000).
- In porcine studies, chronic ipamorelin administration increased body weight gain and lean mass relative to controls, consistent with the downstream anabolic effects of sustained GH elevation.
- In the context of postoperative ileus (POI), ipamorelin restored gut motility in rodent models of surgical ileus — the preclinical signal that motivated the clinical programme.
Drawbacks and concerns
- Ipamorelin's clinical development programme for postoperative ileus failed: the Phase 2 proof-of-concept trial (Beck et al.) found no significant benefit over placebo on the primary endpoint, and the Phase 3 programme was terminated — the one indication rigorously tested in humans was not supported.
- No approved human indication exists for ipamorelin in any country; it is not licensed by the FDA, EMA, or any equivalent regulator for any use.
- The FDA issued a guidance in 2023 clarifying that ipamorelin and several other peptides are not eligible for use in compounded preparations — a significant shift in the US regulatory landscape that affects clinical access as well as grey-market sales.
- While ipamorelin is more selective than earlier GHSs, GH elevation over any sustained period carries the same class risks: potential insulin resistance, fluid retention, and theoretical promotion of pre-existing neoplastic lesions via IGF-1 elevation.
- Human data on repeated subcutaneous dosing — the route and schedule used by self-experimenters — consists only of Phase 2 clinical trial data in hospitalised patients; the long-term safety of chronic outpatient use is unstudied.
- Grey-market ipamorelin purity and concentration accuracy are unverified; no pharmaceutical manufacturing standard applies to research-chemical sources.
Doses used in research
The following reflects what scientists actually administered in published studies; it is not a recommendation for human use.
- Raun 1998 discovery / characterisation study (Eur J Endocrinol): Ipamorelin approximately 3 nmol/kg intravenously in anaesthetised pigs, as part of the dose-response characterisation establishing ipamorelin's GH selectivity versus GHRP-6 and GHRP-2.
- Gobburu 1999 Phase 1 healthy volunteer PK/PD study: Ipamorelin 0.1, 1, and 10 µg/kg single intravenous doses in healthy adult volunteers to characterise pharmacokinetics, GH response, and cortisol selectivity.
- Beck POI Phase 2/3 clinical programme: Ipamorelin 0.03 mg/kg (30 µg/kg) intravenously twice daily in postoperative patients, beginning the morning after bowel surgery, to assess restoration of GI motility.
These doses are from published research only. No safe or effective dose has been established for human use of ipamorelin outside clinical trial settings, and ipamorelin is not approved for human use by any regulatory authority.
Safety and limitations
The most important signal from ipamorelin's development history is the failure of the postoperative ileus programme. The Phase 2 proof-of-concept trial found no significant benefit over placebo; a subsequent Phase 3 programme also did not meet primary endpoints and was terminated. Ipamorelin raises GH in humans as predicted — the PK/PD data confirm that — but GHS-R1a agonism was insufficient to produce a detectable clinical benefit in the one indication where it was rigorously tested.
Within clinical trials, ipamorelin was well tolerated at the tested doses. No serious safety signals beyond those expected from transient GH elevation were reported, and the cortisol/ACTH selectivity observed preclinically appears to hold in humans. However, the safety database is limited to short-duration trials (days to a few weeks) in surgical patients. Chronic self-administration over months or years — as seen in bodybuilding and biohacking contexts — has never been studied in a controlled setting. Repeated GH/IGF-1 elevation carries theoretical long-term risks including insulin resistance, fluid retention, and, speculatively, effects on cell proliferation in individuals with occult malignancy.
Common online claims for ipamorelin — muscle gain, fat loss, anti-aging, improved sleep — are not supported by completed peer-reviewed human RCTs. Ipamorelin raises GH; GH has anabolic effects; but translating acute GH pulses into meaningful body composition changes in healthy, non-GH-deficient adults is a separate and harder question that has not been answered for this compound. Ghrelin receptor agonism can also stimulate appetite, a class effect not always highlighted in promotional material.
Ipamorelin is not approved anywhere. Research chemical preparations sold online are unregulated — purity, sterility, and actual peptide content cannot be verified — and no established efficacious dose exists for any human indication.
Sources
- Raun K. et al. "Ipamorelin, the first selective growth hormone secretagogue." European Journal of Endocrinology, 1998;139(5):552–561. PubMed 9849822
- Gobburu J.V.S. et al. "Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers." Journal of Pharmacology and Experimental Therapeutics, 1999;291(1):245–252. PubMed 10496658
- Beck D.E. et al. "Prospective, randomized, controlled, proof-of-concept study of the Ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients." Diseases of the Colon & Rectum, 2014;57(12):1403–1411. PubMed 25331030
- Johansen P.B. et al. "Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats." Growth Hormone & IGF Research, 1999;9(2):106–113. PubMed 10373343
- Svensson J. et al. "The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats." European Journal of Endocrinology, 2000;142(1):78–84. PubMed 10828840
- Andersen N.B. et al. "The growth hormone secretagogue ipamorelin counteracts glucocorticoid-induced decrease in bone formation of adult rats." European Journal of Endocrinology, 2001;144(5):541–546. PubMed 11735244
- Raun K. et al. "Pharmacokinetic evaluation of ipamorelin and other peptidyl growth hormone secretagogues with emphasis on nasal absorption." European Journal of Drug Metabolism and Pharmacokinetics, 1998. PubMed 9879640 (cite-only)
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