Ipamorelin: selective growth-hormone-releasing peptide
A synthetic five-amino-acid peptide developed at Novo Nordisk that triggers growth hormone release from the pituitary gland without raising stress hormones like cortisol; experimental, not an approved drug.
- Class
- Selective growth hormone secretagogue (GHS-R1a / ghrelin-receptor agonist), pentapeptide
- Status
- Investigational; not FDA-approved for any indication; WADA-prohibited at all times under class S2.
- Best-supported effect
- Selective pulsatile growth hormone release in human PK/PD studies, without significant elevation of cortisol, prolactin, ACTH, or aldosterone at studied doses.
- Main caveat
- No completed Phase III program, no approved indication, and no long-duration human trials of body composition, sleep, recovery, or anti-aging endpoints.
A researcher, an agent, or an algorithm wrote down the sequence and picked a target to hit.
An AI model like OpenFold3 or AlphaFold built a 3D structure and scored how well it fits the binding site.
A second contributor repeated the computation on their own hardware and the scores matched.
FDA-tracked compound — synthesized for clinical/research use
Fork this card to add platform evidence →
FDA-tracked (reclassified Category 1, Feb 2026) — preclinical/clinical bioassay data exists
Fork this card to add platform evidence →
What this is
Ipamorelin is a synthetic five-amino-acid peptide developed at Novo Nordisk in the late 1990s to trigger growth hormone (GH) release from the pituitary gland. What sets it apart from earlier GH-releasing peptides is its selectivity: at concentrations well above those needed to release GH, it does not significantly raise cortisol, prolactin, ACTH, or aldosterone — a profile that no earlier compound in the class could match (Raun et al. 1998). The stored sequence AHWFK is a shorthand — the actual compound is Aib-His-D-2-Naphthylalanine-D-Phe-Lys-NH₂, with an α-aminoisobutyric acid at position 1, D-amino acids at positions 3 and 4, and a C-terminal amide cap; none of these modifications are visible in the five-letter code. Ipamorelin has never been approved for any indication by the FDA or EMA and remains an investigational compound. It is prohibited under WADA's S2 category at all times.
History
Ipamorelin (internal code NNC 26-0161) was first described in the peer-reviewed literature in 1998 by Raun and colleagues at Novo Nordisk (European Journal of Endocrinology). It emerged from a medicinal-chemistry effort to improve on the earlier growth hormone-releasing peptides — GHRP-6, GHRP-2, hexarelin — by eliminating the cortisol, ACTH, and prolactin elevation that limited their clinical utility. The Novo Nordisk program screened pentapeptide variants and identified the Aib-His-D-2-Nal-D-Phe-Lys-NH₂ sequence as retaining potent GHS-R1a agonism while showing no significant hormonal off-target effects even at doses far above the effective GH-releasing range, in both pig and rat models. Novo Nordisk conducted early human pharmacokinetic and pharmacodynamic trials but did not advance the compound to a regulatory submission. The program was later licensed to Helsinn / Sapphire Therapeutics, which ran a Phase IIb randomized controlled trial in postoperative ileus (published by Beck and colleagues in 2014); that trial trended toward faster gastrointestinal recovery but did not advance to Phase III. Ipamorelin subsequently became widely discussed in research-peptide and compounding-pharmacy channels, frequently paired in descriptions with CJC-1295 because the two peptides act on mechanistically independent receptor pathways.
What it does
Ipamorelin mimics ghrelin, a gut-derived hormone that also triggers GH release from the pituitary. It binds the GHS-R1a receptor on anterior pituitary cells and causes a pulsatile burst of GH secretion — preserving the natural rhythm of GH release rather than producing a sustained flat elevation. Because its receptor pathway is independent from the one used by GHRH analogs such as CJC-1295 and sermorelin, the two classes of secretagogues can produce a larger combined GH pulse than either alone. In animal studies, ipamorelin also shows effects on gastric motility and counteracts glucocorticoid-driven reductions in bone formation (Venkova et al. 2009; provenance data). The key clinical limitation is that GH release in pharmacological studies does not automatically translate into improved body composition, sleep architecture, or recovery in long-duration human endpoint trials — none of which have been conducted for ipamorelin.
Evidence
- Human: Phase I pharmacokinetic and pharmacodynamic studies established dose-dependent pulsatile GH release with a selectivity profile in healthy volunteers (Gobburu and colleagues, 1999, Pharmaceutical Research). A single Phase IIb randomized controlled trial in adults undergoing bowel resection (N=114; Beck and colleagues, 2014) trended toward faster postoperative GI recovery but did not reach its primary endpoint decisively and the program was discontinued. No Phase III trials and no approved indication exist. Body composition, sleep, recovery, and anti-aging endpoints have not been evaluated in long-duration controlled human trials of ipamorelin.
- Animal: Selective GH release without cortisol, prolactin, or ACTH elevation established in swine (Raun et al. 1998). Longitudinal bone growth in rats (provenance data). Counteraction of glucocorticoid-induced bone-formation decrease in adult rats (provenance data). Prokinetic effects in rodent postoperative ileus models (Venkova et al. 2009). Increased bone mineral content in adult female rats alongside GHRP-6 (provenance data).
- In vitro / receptor: GHS-R1a binding and signaling characterized; shown to act as an orthosteric super-agonist at the ghrelin receptor, activating Gαo1 without allosteric modulation (Bennett et al. 2009). The GHSR established as the physiologically relevant ghrelin receptor mediating GH release and appetite signals (Sun et al. 2004).
Known effects
- Pulsatile GH release — Phase I human PK/PD data (Gobburu 1999); well-established
- Hormonal selectivity (no significant cortisol / prolactin / ACTH / aldosterone elevation at studied doses) — Human PK/PD and swine studies (Raun et al. 1998); the compound's defining pharmacological feature
- Prokinetic (GI motility) — Preclinical and one Phase IIb trend (Venkova et al. 2009; Beck et al. 2014); not confirmed at Phase III
- Bone formation support — Preclinical only (longitudinal bone growth, bone mineral content, glucocorticoid-counteraction studies); no human endpoint trial
- IGF-1 elevation — Expected downstream consequence of GH release; magnitude and long-term implications not characterized in controlled human studies
- Body composition, lean mass, fat loss — Plausible from GH/IGF-1 pharmacology; not tested in long-duration controlled human endpoint trials
- Sleep quality improvement — Commonly reported anecdotally; no controlled sleep-architecture trial of ipamorelin identified
Safety signals
Published human and animal data identify the following signals:
- Increased appetite / hunger — Predictable consequence of ghrelin-receptor activation
- Mild water retention, transient flushing, head rush, headache, injection-site reactions — Reported in compiled clinical descriptions as generally mild and dose-related; described in available literature as a cleaner tolerability profile than older GHRPs
- Nausea — Reported in the Phase IIb trial: 33.9% of ipamorelin-treated patients (N=56) vs. the placebo arm (Beck et al. 2014)
- Cortisol, prolactin, ACTH, FSH, LH, TSH — No significant change at studied doses; this selectivity finding is central to ipamorelin's pharmacological profile (Raun et al. 1998)
- IGF-1 elevation — Expected; underlies theoretical concerns about chronic IGF-1 exposure and proliferative risk
- Glycemic effects — GH opposes insulin action; class-level concern; available literature describes a milder profile for ipamorelin than for MK-677
- Long-term safety — No controlled chronic human safety data; chronic use patterns exist largely outside controlled trials
- PCAC October 2024 decision — The FDA Pharmacy Compounding Advisory Committee voted against adding ipamorelin to the 503A bulk substances list, citing concerns including fluid retention, congestive heart failure risk, and hyperglycemia
Regulatory status
- US (FDA): Not approved for any indication. The FDA PCAC voted in October 2024 against 503A bulk-list inclusion, narrowing legitimate compounding access.
- EU (EMA) / UK (MHRA): Not authorized as a medicine.
- Canada: Unapproved investigational agent.
- Australia (TGA): GH secretagogues are classified as Schedule 4 prescription-only; class-level statement.
- WADA: Prohibited at all times under S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics). LC-MS/MS detection methods for ipamorelin and its metabolites in urine are established (Thevis and colleagues, doping-control literature).
- DEA (US): Not scheduled under the Controlled Substances Act.
Mechanism
Ipamorelin is a selective agonist at GHS-R1a, the ghrelin receptor expressed on anterior-pituitary somatotrophs. Bennett and colleagues (2009, Molecular Pharmacology) characterized it as an orthosteric super-agonist that activates Gαo1 signaling at the receptor; separately, the ghrelin receptor has been shown to be the physiologically relevant mediator of GH release and appetite responses to ghrelin-class ligands (Sun et al. 2004, PNAS). Receptor activation engages Gαq/11–phospholipase C signaling, hydrolyzing PIP₂ to IP₃ and DAG, mobilizing intracellular calcium, and triggering pulsatile GH vesicle release from somatotrophs. Because GHS-R1a signaling is independent of the GHRH receptor pathway (which signals via Gαs/cAMP/PKA), ipamorelin and GHRH analogs can be co-administered to produce a larger combined GH pulse — a synergistic interaction at the receptor-pathway level. The selectivity first reported by Raun and colleagues (1998) in swine — GH release without cortisol, prolactin, ACTH, FSH, LH, TSH, or aldosterone elevation at studied doses — is the compound's pharmacological signature. Animal mechanistic work also documents counteraction of glucocorticoid-induced suppression of bone formation and prokinetic effects at GHS-R1a receptors in the enteric nervous system, consistent with peripheral expression of the receptor.
Open questions
- Long-term human safety: No completed long-duration controlled human safety program exists for any population; consequences of chronic IGF-1 elevation are theoretical rather than characterized for ipamorelin specifically.
- Clinical efficacy beyond GH release: Whether the selectivity advantage and pulsatile GH release translate into body composition, sleep, recovery, or bone-density endpoints has not been tested in controlled human trials.
- Postoperative ileus and cachexia: The Phase IIb program was discontinued after a non-decisive readout; whether refined patient selection or dosing could support a renewed clinical pathway is unresolved.
- GHRH-analog combination pharmacology in humans: The CJC-1295 + ipamorelin combination rests on independent-receptor pharmacology; controlled human endpoint trials of the combination are not available.
- Sequence verification: Available literature contains two notations for the position-3 residue (D-2-naphthylalanine vs. D-tryptophan) in different sources; Raun et al. (1998) is the primary reference.
- Tachyphylaxis: Theoretical desensitization with chronic GHS-R1a agonism has not been quantified for ipamorelin in long-duration human studies.
- Compounding access pathway: Following the October 2024 PCAC vote against 503A inclusion, the US legitimate clinical-access pathway has narrowed; current regulatory status should be verified against FDA guidance.
Related peptides
- CJC-1295 — GHRH analog acting at the mechanistically independent GHRH receptor; frequently co-described with ipamorelin for dual-pathway GH stimulation
- Sermorelin — shorter-acting GHRH analog; same independent-receptor pharmacology rationale as CJC-1295 for combination use
Research directions for this peptide, selected from the current sources — hypotheses you can explore and model. None of it is proven yet; tap any one to see the full thinking.
Could a bulky ring-shaped amino acid do the same job as a fatty acid chain when binding to the growth hormone receptor?
If true, we could design new growth hormone boosting peptides that do not need special enzymes to add a fat tag, making them easier and cheaper to produce as medicines.
Could the mirror-image shape of two building blocks in ipamorelin prevent it from flipping the switch for stress hormones, while still flipping the switch for growth hormone?
If true, doctors could one day use growth hormone treatments without worrying about raising stress hormones, which is a major safety problem with current alternatives.
Could this peptide help the digestive system wake up faster after an operation, not just by releasing growth hormone but by acting directly on gut nerves?
If true, patients recovering from abdominal surgery could leave the hospital sooner with less nausea and bloating, because their digestive systems would restart faster.
Could a peptide that boosts growth hormone without raising stress hormones help cancer patients keep their muscle strength?
If true, cancer patients losing weight and strength could have a safer option to maintain muscle, because current alternatives that also raise stress hormones can actually make muscle loss worse.
Could scientists attach an extra therapeutic feature to this short peptide while keeping its growth hormone boosting ability intact?
If true, one injection could deliver two treatments at once, such as muscle building plus anti-inflammatory or bone repair effects, making therapy simpler and more powerful.
Could a small chemical cap at the end of a short peptide help it stay attached to its target longer than natural versions?
If true, this simple cap trick could be copied to make other short-acting peptide drugs last longer in the body, reducing how often patients need injections.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.9786232709884644 | boltz-2 |
| ranking score | 0.8462891578674316 | boltz-2 |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 0.469 | global PDE — lower = better |
| disorder | NaN | fraction disordered |
▸3-letter notation
▸recipeboltz-2 1.0
| parameter | value |
|---|---|
| model | boltz-2 1.0 |
| weights | — |
| hardware | nvidia_nim_api |
| mlx version | — |
| python | — |
| random seed | — |
| msa strategy | none |
| diffusion samples | 1 |
| runtime | — |
| predicted by | mlx@peptide |
| predicted at | 2026-04-24 |
▸citationbibtex
@peptide{pep00019,
sequence = {AHWFK},
target = {ghsr},
author = {peptidemodel},
year = {2026},
status = {bioassayed}
}