Ipamorelin (NNC 26-0161) Evidence Grade: A-
Ipamorelin is a synthetic pentapeptide growth hormone secretagogue (GHS) that selectively stimulates growth hormone (GH) release from the anterior pituitary by activating the ghrelin receptor (GHS-R1a). It is distinguished from other GH secretagogues by its remarkable selectivity, producing robust GH pulses without significantly elevating cortisol, prolactin, or ACTH levels, an attribute that has made it one of the most widely studied peptides in growth hormone research.
Developed by Novo Nordisk in the late 1990s, Ipamorelin was investigated clinically for postoperative ileus recovery and has since become a cornerstone research compound in GH axis studies. Its clean pharmacological profile and well-characterized dose-response relationship make it a reference standard for evaluating selective GH secretion.
Table of Contents
Overview & Introduction
Ipamorelin (developmental code NNC 26-0161) is a synthetic pentapeptide consisting of five amino acids (Aib-His-D-2-Nal-D-Phe-Lys-NH2) that functions as a potent and selective growth hormone secretagogue. It belongs to the class of growth hormone releasing peptides (GHRPs) but is pharmacologically distinct due to its high selectivity for GH release over other pituitary hormones.
The peptide acts as an agonist at the growth hormone secretagogue receptor type 1a (GHS-R1a), also known as the ghrelin receptor, which is expressed on somatotroph cells in the anterior pituitary gland. Upon receptor activation, Ipamorelin triggers a signaling cascade that results in the exocytotic release of stored growth hormone. Unlike less selective GHRPs such as GHRP-6, Ipamorelin does not meaningfully activate ACTH or cortisol secretion at doses that produce maximal GH release.
This selectivity profile was first characterized in detail by Raun et al. (1998) in a landmark study that compared Ipamorelin head-to-head with GHRP-6, GHRP-2, and hexarelin across multiple dose levels. The study demonstrated that even at doses 200-fold above the ED50 for GH release, Ipamorelin did not stimulate ACTH or cortisol secretion, establishing it as the most selective GHS identified at that time. This finding has been consistently replicated in subsequent studies and forms the basis for its widespread use in research.
The molecular weight of Ipamorelin is approximately 711.85 Da, placing it in the small peptide category. Its compact size contributes to favorable pharmacokinetic properties including rapid absorption from subcutaneous injection sites, a half-life of approximately 2 hours, and predictable dose-response relationships across species.
History & Discovery
Development at Novo Nordisk. Ipamorelin was synthesized and characterized as part of a systematic effort to develop selective GH secretagogues. The compound was designed through structure-activity relationship studies starting from the growth hormone releasing peptide scaffold, with modifications aimed at eliminating cortisol and prolactin stimulation while retaining GH secretory potency.
Landmark selectivity study published. Raun et al. published the definitive characterization of Ipamorelin in the European Journal of Endocrinology, demonstrating its unprecedented selectivity for GH release over ACTH and cortisol. This study established the pharmacological benchmark for GHS selectivity (PMID: 9820627).
Clinical development for postoperative ileus. Helsinn Therapeutics licensed Ipamorelin and advanced it into Phase II/III clinical trials for the treatment of postoperative ileus (delayed bowel motility following surgery). These trials represented the most extensive human safety and efficacy data generated for the compound.
Clinical trial results and discontinuation. While Ipamorelin showed promising signals for accelerating GI recovery post-surgery, the Phase III program did not meet all primary endpoints. Clinical development was discontinued, though the extensive safety database from these trials remains valuable.
Research compound adoption. Ipamorelin became widely adopted in research settings for studying GH axis physiology, body composition, and aging-related GH decline. Its clean selectivity profile makes it a preferred tool for isolating GH-specific effects.
Mechanism of Action
Ipamorelin exerts its primary biological effect through selective agonism of the growth hormone secretagogue receptor type 1a (GHS-R1a). This mechanism is distinct from growth hormone releasing hormone (GHRH) and operates through a complementary signaling pathway.
Ipamorelin binds to GHS-R1a on anterior pituitary somatotroph cells, activating the Gq/11-phospholipase C signaling cascade. This triggers inositol trisphosphate (IP3)-mediated calcium release from intracellular stores, raising cytosolic calcium concentrations. The calcium influx stimulates the fusion of GH-containing secretory granules with the plasma membrane, resulting in pulsatile GH release. This mechanism is additive with GHRH signaling, which operates through cAMP-dependent pathways.
Unlike GHRP-6 and hexarelin, Ipamorelin does not significantly activate corticotroph cells (ACTH-secreting) or lactotroph cells (prolactin-secreting) in the pituitary. This selectivity appears to be related to its specific binding conformation at GHS-R1a, which favors the Gq pathway in somatotrophs while minimizing cross-activation of adjacent cell populations. At standard research doses, cortisol and prolactin levels remain at baseline during Ipamorelin-stimulated GH pulses.
Ipamorelin amplifies the amplitude of GH pulses while preserving the endogenous pulsatile secretion pattern. It works synergistically with endogenous GHRH and is subject to negative feedback by somatostatin. This means the peptide does not override the hypothalamic-pituitary regulatory axis but rather enhances its output within physiological constraints. The resulting GH profile more closely resembles youthful secretion patterns than exogenous GH administration.
The GH pulses stimulated by Ipamorelin drive hepatic production of insulin-like growth factor 1 (IGF-1), the primary mediator of many GH-dependent anabolic and regenerative effects. IGF-1 levels rise in a dose-dependent manner following repeated Ipamorelin administration, though they typically remain within the upper physiological range rather than reaching supraphysiological levels seen with exogenous GH injection.
Research Applications
GH Axis Physiology
Ipamorelin serves as a pharmacological tool for studying GH secretion dynamics, pulsatility, and feedback mechanisms. Its selectivity allows researchers to isolate GH-specific effects without confounding changes in cortisol or prolactin, making it invaluable for endocrine research protocols.
Body Composition Studies
Research protocols have utilized Ipamorelin to study GH-mediated changes in body composition, including lean mass accretion, fat metabolism, and nitrogen balance. Animal studies demonstrate dose-dependent increases in lean body mass and reductions in adiposity with chronic administration.
Bone Density Research
The GH-IGF-1 axis is a major regulator of bone metabolism. Ipamorelin has been studied in ovariectomized rat models of osteoporosis, where it demonstrated significant increases in bone mineral density and cortical bone strength. These studies suggest potential applications in age-related bone loss research.
Gastrointestinal Motility
Ipamorelin's clinical development focused on postoperative ileus, reflecting the role of ghrelin receptor activation in promoting GI motility. The peptide accelerates gastric emptying and colonic transit time, mediated partly through vagal afferent pathways and partly through direct effects on GI smooth muscle.
Age-Related GH Decline
The somatopause, the progressive decline in GH secretion with aging, is a major research focus. Ipamorelin provides a model for restoring youthful GH pulsatility without supraphysiological hormone levels, making it relevant to gerontological research.
Clinical Evidence
Selectivity and Dose-Response Characterization
Raun et al. (1998) conducted the definitive pharmacological characterization of Ipamorelin in swine and rat models. The study demonstrated that Ipamorelin stimulated GH release with an ED50 of 80 nmol/kg IV in swine, while ACTH and cortisol levels remained unchanged even at doses 200-fold above the GH ED50. Head-to-head comparison showed GHRP-6 and GHRP-2 elevated cortisol at doses just 2-5 fold above their GH ED50 values.
PMID: 9820627
Clinical Trial in Postoperative Ileus
Beck et al. (2008) reported results from a Phase II randomized, double-blind, placebo-controlled trial of Ipamorelin for postoperative ileus following abdominal surgery. The study enrolled over 100 patients and evaluated time to first bowel movement, length of hospital stay, and GH/IGF-1 levels. Ipamorelin treatment was associated with accelerated GI recovery and was well-tolerated, with an adverse event profile comparable to placebo.
PMID: 18363475
Bone Anabolic Effects
Svensson et al. (2000) investigated Ipamorelin's effects on bone metabolism in adult rats. Chronic Ipamorelin administration produced dose-dependent increases in bone formation markers, cortical bone mineral content, and periosteal bone formation. The effects were comparable to exogenous GH treatment, supporting a mechanism mediated through the GH-IGF-1 axis.
PMID: 10852480
GH Release Pharmacokinetics in Humans
Gobburu et al. (1999) developed a pharmacokinetic-pharmacodynamic model for Ipamorelin-stimulated GH release in healthy human volunteers. The study characterized the dose-response relationship, demonstrating saturable GH release kinetics and confirming that GH pulses returned to baseline within 2-3 hours, consistent with physiological pulsatile secretion patterns.
PMID: 10344583
Body Composition in GH-Deficient Models
Johansen et al. (1999) evaluated Ipamorelin's effects on body composition in a rat model of growth hormone deficiency. Treatment resulted in significant increases in body weight gain (lean mass) and tibial growth plate width, confirming that the GH released by Ipamorelin is biologically active and capable of mediating growth-promoting effects at the tissue level.
PMID: 10421769
Dosing Protocols (Research Context)
Research Use Only: The following dosing information is derived from published research and clinical trials. Ipamorelin is not approved for therapeutic use. All protocols are for educational reference.
| Parameter | Research Protocol |
|---|---|
| Standard Research Dose | 100-300 mcg per administration |
| Frequency | 1-3 times daily (mimicking GH pulse frequency) |
| Optimal Timing | Morning fasted, post-workout, and/or before sleep |
| Protocol Duration | 8-12 weeks typical in research contexts |
| Route | Subcutaneous injection |
| Dose Ceiling | ~1 mcg/kg produces near-maximal GH response |
Dose-Response Considerations
Clinical pharmacokinetic studies demonstrate a saturable dose-response curve for GH release. Doses above approximately 1 mcg/kg body weight do not produce proportionally greater GH pulses, indicating receptor saturation. This ceiling effect provides a natural limit on GH stimulation and is one mechanism by which Ipamorelin maintains a favorable safety profile.
Timing relative to food intake matters: insulin and glucose elevation blunt the GH response to Ipamorelin. Research protocols typically specify administration during fasted states or at least 90 minutes after meals to maximize GH pulse amplitude.
Administration & Reconstitution
Reconstitution Protocol
Ipamorelin is supplied as a lyophilized (freeze-dried) powder, typically in vials containing 2 mg or 5 mg of peptide. Reconstitution requires bacteriostatic water (BAC water) for multi-use preparations.
| Vial Size | BAC Water Volume | Concentration |
|---|---|---|
| 2 mg | 2 mL | 1 mg/mL (1000 mcg/mL) |
| 5 mg | 2.5 mL | 2 mg/mL (2000 mcg/mL) |
| 5 mg | 5 mL | 1 mg/mL (1000 mcg/mL) |
Injection Technique
- Use insulin syringes (29-31 gauge, 0.5 mL or 1 mL)
- Inject subcutaneously into abdominal fat pad, rotating injection sites
- Pinch skin and inject at 45-degree angle
- Allow BAC water to run down the inside of the vial during reconstitution; do not shake or jet directly onto the lyophilized cake
- Gently swirl until fully dissolved; solution should be clear and colorless
Side Effects & Safety Profile
Ipamorelin has demonstrated a favorable safety profile across both preclinical studies and clinical trials. The Phase II/III clinical trial program for postoperative ileus generated the most extensive human safety data, with adverse event rates comparable to placebo.
Common (Mild)
- Transient injection site redness or irritation
- Mild headache (typically resolves within hours)
- Transient flushing or warmth sensation
- Mild lightheadedness post-injection
Uncommon / Rare
- Water retention (dose-dependent, usually mild)
- Tingling or numbness in extremities
- Mild appetite increase
- Joint stiffness at higher doses
Safety Advantages vs. Other GH Secretagogues
Ipamorelin's key safety advantage is the absence of cortisol and prolactin stimulation. Elevated cortisol can impair immune function, promote fat storage, and cause anxiety, while prolactin elevation can cause sexual dysfunction and gynecomastia. By avoiding these off-target effects, Ipamorelin maintains a cleaner side effect profile than GHRP-6, GHRP-2, or hexarelin at equivalent GH-stimulating doses.
Unlike exogenous GH, Ipamorelin does not suppress endogenous GH production. The pulsatile release pattern and somatostatin feedback regulation are preserved, reducing the risk of hypothalamic-pituitary axis suppression upon discontinuation.
Stacking & Combinations
Ipamorelin + CJC-1295 (no DAC)
The most widely studied combination pairs Ipamorelin (GHS-R1a agonist) with CJC-1295 without DAC, also known as Modified GRF 1-29 (GHRH analog). The rationale is mechanistic synergy: CJC-1295 amplifies GH pulse amplitude through cAMP-dependent pathways, while Ipamorelin triggers the pulse through IP3/calcium signaling. Co-administration produces GH pulses significantly larger than either compound alone. Typical research protocol: 100 mcg CJC-1295 no DAC + 100-200 mcg Ipamorelin, administered simultaneously.
Ipamorelin + GHRH Analogs
The synergy between GHS and GHRH analogs is well-documented in the literature. Sermorelin or tesamorelin may also be combined with Ipamorelin for similar amplification effects. The combination approach allows lower doses of each individual compound while achieving greater GH release.
Ipamorelin + BPC-157
Some research protocols combine Ipamorelin with BPC-157 for tissue repair applications. The rationale is that Ipamorelin upregulates GH receptor expression via GH-IGF-1 axis stimulation, potentially enhancing BPC-157's growth factor-mediated repair pathways. This combination targets both systemic (GH/IGF-1) and local (tissue repair) healing mechanisms.
Compounds to Avoid Combining
Ipamorelin should not be combined with somatostatin analogs (e.g., octreotide) as these directly antagonize GH release. High-dose insulin administration may blunt the GH response. Concurrent exogenous GH use reduces the utility of Ipamorelin, as the negative feedback from supraphysiological GH levels suppresses endogenous GH secretion pathways.
Storage & Stability
| Form | Storage Conditions | Stability Duration |
|---|---|---|
| Lyophilized Powder | Refrigerated (2-8°C / 36-46°F) | 24+ months |
| Lyophilized Powder | Room Temperature (up to 25°C) | 3-6 months |
| Lyophilized Powder | Frozen (-20°C) | 36+ months |
| Reconstituted (BAC Water) | Refrigerated (2-8°C) | 21-28 days |
| Reconstituted (Sterile Water) | Refrigerated (2-8°C) | 48-72 hours |
Handling Guidelines
- Protect from light exposure at all times
- Do not freeze reconstituted peptide solutions
- Avoid repeated freeze-thaw cycles of lyophilized powder
- Discard reconstituted solution if cloudiness, discoloration, or particulates are observed
- Use bacteriostatic water (0.9% benzyl alcohol) for multi-dose reconstitution
Regulatory Status
Ipamorelin is classified as a research compound and is not approved by the FDA, EMA, or any regulatory agency for human therapeutic use. Its regulatory history reflects its journey through clinical development and subsequent positioning as a research-only peptide.
- United States: Not FDA-approved. Available for research purposes. Not currently scheduled under the Controlled Substances Act. Subject to compounding pharmacy regulations.
- European Union: Not EMA-approved. Available as a research chemical. Regulatory status varies by member state.
- Australia: Listed as a Schedule 4 (Prescription Only) substance by the TGA. Prohibited in sport by WADA.
- WADA Status: Prohibited at all times under the category of Growth Hormone Secretagogues (S2 section of the Prohibited List).
- Clinical Development: Phase III clinical trials for postoperative ileus were completed but did not lead to regulatory approval. The compound is no longer under active pharmaceutical development.
Frequently Asked Questions
What makes Ipamorelin different from other GH secretagogues?
How quickly does Ipamorelin elevate GH levels?
Can Ipamorelin be combined with CJC-1295?
Does Ipamorelin increase appetite like GHRP-6?
References
- Raun K, et al. "Ipamorelin, the first selective growth hormone secretagogue." Eur J Endocrinol. 1998;139(5):552-561. PMID: 9820627
- Beck DE, et al. "Ipamorelin for the treatment of postoperative ileus." J Surg Res. 2008. PMID: 18363475
- Svensson J, et al. "The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats." J Endocrinol. 2000;165(3):569-577. PMID: 10852480
- Gobburu JV, et al. "Pharmacokinetic-pharmacodynamic modeling of ipamorelin." J Clin Pharmacol. 1999;39(1):67-75. PMID: 10344583
- Johansen PB, et al. "Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats." Growth Horm IGF Res. 1999;9(2):106-113. PMID: 10421769
Related Pages
Concise compound overview with dosing tables
Step-by-step research protocol
Oral GH secretagogue deep-dive
GHRH analog for synergy stacking
Precise dosing for any vial size
Pre/post protocol lab panels
Medical Disclaimer: This article is provided for educational and research reference purposes only. It does not constitute medical advice, diagnosis, or treatment recommendations. Ipamorelin is not approved by the FDA or any regulatory agency for human use. All information is derived from preclinical and clinical research and should not be interpreted as clinical guidance. Consult a qualified healthcare professional before considering any research compound. See our full Medical Disclaimer.
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