Ipamorelin --- Research Product Overview

**Disclaimer:** This article is provided for educational and research purposes only. [Ipamorelin](/research/ipamorelin-ghrelin-mimetic) research material sold by Viking Labs is intended for laboratory research use only and is not approved by the FDA for human therapeutic use. Nothing in this article constitutes medical advice or a recommendation for self-administration.

Overview

Ipamorelin is a synthetic pentapeptide growth-hormone secretagogue (GHS) and a selective agonist at the growth-hormone secretagogue receptor type 1a (GHSR-1a, the ghrelin receptor). It was developed at Novo Nordisk in the 1990s as part of a research program aimed at identifying small synthetic peptides that could selectively stimulate growth hormone (GH) release without the broader pituitary effects of older GHS compounds. Ipamorelin is notable in the GHS literature for its high selectivity for GH release, with minimal effects on prolactin, ACTH, cortisol, FSH, LH, or TSH at GH-stimulating doses in preclinical studies. For broader context on the receptor system, see our growth hormone axis and ipamorelin ghrelin mimetic reference articles.

The peptide is widely used as a reference GHSR-1a agonist in laboratory growth hormone axis research.

Sequence and Structural Notes

Ipamorelin sequence: H-Aib-His-D-2-Nal-D-Phe-Lys-NH2

The peptide contains two non-natural residues: alpha-aminoisobutyric acid (Aib) at position 1 and 2-naphthylalanine in the D-configuration (D-2-Nal) at position 3. The D-Phe at position 4 and the C-terminal amide further enhance proteolytic stability. Molecular weight: approximately 711.9 Da. Molecular formula: C38H49N9O5.

The compact, stabilized structure is responsible for the peptide's resistance to peptidase degradation and contributes to a working in vivo half-life of approximately 2 hours in rodents (Raun et al., 1998).

Mechanism of Action

Ipamorelin acts as a full agonist at GHSR-1a, the same receptor activated by endogenous ghrelin. GHSR-1a is a Gq-coupled GPCR expressed prominently on somatotrophs of the anterior pituitary, where it activates phospholipase C, IP3, and DAG signaling, increasing intracellular calcium and triggering pulsatile growth hormone release. Unlike growth hormone-releasing hormone (GHRH), which acts via the GHRHR/cAMP pathway, GHSR-1a engagement uses a complementary signaling axis --- which is the rationale for studying GHRH-class and GHS-class peptides in combination.

The selectivity of ipamorelin for GH over ACTH/cortisol distinguishes it from earlier GHS compounds (e.g., GHRP-6, hexarelin), which produce more substantial cortisol elevations. This selectivity has made ipamorelin a useful tool for dissecting GHSR-1a-specific effects in research models.

Comparator Peptides --- Ipamorelin vs. GHRP-6 vs. CJC-1295

Ipamorelin sits within a family of synthetic GH secretagogues, but its selectivity profile and pharmacokinetics distinguish it from earlier-generation peptides commonly studied in parallel.

Ipamorelin vs. GHRP-6. GHRP-6 is the second-generation hexapeptide GHSR-1a agonist (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, ~873 Da) that historically anchored the discovery of the GHS receptor system. Both peptides are GHSR-1a full agonists with comparable in vitro receptor potency (low nanomolar EC50 in calcium mobilization assays), but GHRP-6 produces substantially greater elevations in prolactin, ACTH, and cortisol at GH-equivalent doses. The mechanism of GHRP-6's "off-target" pituitary effects is incompletely characterized but appears to involve weak interactions with melanocortin and CRH-related pathways. Ipamorelin's pentapeptide scaffold and non-natural D-residues confer cleaner GHSR-1a selectivity, making it the preferred reference compound for receptor-specific mechanistic studies.

Ipamorelin vs. CJC-1295. CJC-1295 (without DAC, also called Mod-GRF(1-29), ~3367 Da) is a GHRH analogue that activates a different receptor entirely --- GHRHR (Gs-coupled, cAMP-driven) on the somatotroph. The two peptides are not direct comparators in receptor terms but are mechanistically complementary: ipamorelin drives the acute exocytotic release of pre-stored GH via Gq/IP3/calcium, while CJC-1295 drives GH gene transcription and synthesis via Gs/cAMP/PKA. Combining the two produces synergistic GH pulses in preclinical models that exceed either single agent (see the Ipamorelin / CJC-1295 blend overview for detail).

Ipamorelin vs. hexarelin. Hexarelin is another GHSR-1a hexapeptide with greater potency than GHRP-6 but also greater off-target cortisol elevation; ipamorelin is preferred when receptor selectivity is the priority.

Deeper Preclinical Breakdown

Raun et al. (1998) --- foundational characterization (Eur J Endocrinol). This paper established ipamorelin's selectivity profile across multiple species. Methodology: in vitro GH release was measured in rat pituitary cell preparations dosed at 0.1-1000 nM ipamorelin, with parallel measurements of prolactin, ACTH, FSH, LH, and TSH from the same cells; in vivo studies dosed pentobarbital-anesthetized rats at 5-200 microgram/kg IV with serial GH and ACTH plasma sampling. Key results: ipamorelin EC50 for GH release was approximately 1.3 nM in vitro, with no significant effect on the other pituitary hormones at doses up to 1 microM; in vivo, peak GH was reached 10-15 minutes post-dose at the higher doses. Limitation: the paper did not directly compare cortisol elevation against GHRP-2 or hexarelin in parallel cohorts, leaving cross-peptide selectivity inferences to subsequent work.

Svensson et al. (2000) --- bone metabolism in growing rats (J Endocrinol). Methodology: female Sprague-Dawley rats received ipamorelin 0.5 mg/kg/day or vehicle subcutaneously for 12 weeks, with paired GHRP-6 dosing arms; bone mineral content (BMC) and bone mineral density (BMD) were measured by DEXA. Key result: ipamorelin produced significant increases in total BMC and BMD vs. vehicle, comparable to GHRP-6 effects, consistent with sustained GH/IGF-1 axis activation. Limitation: only female rats; the study did not measure pulsatile GH release directly to confirm the mechanism.

Lall et al. (2001) --- pulsatile GH release dynamics. Methodology: cannulated rats received single-bolus and chronic-infusion ipamorelin at 5-50 microgram/kg, with high-frequency plasma sampling for GH pulse analysis. Key result: ipamorelin produced discrete GH pulses with preserved natural pulsatile pattern, in contrast to long-acting GHRH analogues that produce a more tonic GH signature. Limitation: the comparison cohort sizes were small (n=6 per arm).

Common Research Applications

• GHSR-1a binding and functional assays (intracellular calcium, IP1 accumulation)
• Studies of pulsatile GH release in rodent and porcine pituitary preparations
• Comparative pharmacology against GHRP-2, GHRP-6, hexarelin, and ghrelin
• GH axis research in aging, catabolic, or fasted models
• Combination studies with GHRH-class peptides (e.g., CJC-1295, sermorelin) to study GHRHR + GHSR-1a synergy
• GI motility models (gastric emptying, intestinal transit)

Formulation Considerations

Lyophilized ipamorelin is supplied as a white powder or amorphous cake from acetate-buffered solution. The peptide is highly water-soluble due to its small size and basic Lys/His residues; reconstitution at 1-5 mg/mL in sterile bacteriostatic water proceeds in seconds with gentle inversion. Sterile saline or PBS pH 6.5-7.5 is also acceptable; ipamorelin is stable across a relatively broad pH range (4-8) due to its non-natural residues and C-terminal amide.

Reconstituted ipamorelin in glass at 2-8 degrees C retains greater than 95% main-peak purity for 14-30 days under aseptic conditions; the small, non-lipidated structure is less prone to surface adsorption than larger peptides. Light-driven degradation is minimal because the peptide lacks Trp and the D-2-Nal naphthyl group is photostable. Common COA impurities include the des-Aib N-terminal truncation product (typically less than 0.5%), the L-2-Nal stereoisomer (typically less than 0.3%), and acetate counterion in the 6-12% range. For broader formulation guidance, see our peptide reconstitution guide and peptide solubility guide.

Research-Context Dosing Ranges

In published preclinical literature, ipamorelin doses in rats have ranged from approximately 5 to 200 microgram/kg administered intravenously, subcutaneously, or intraperitoneally for acute GH release studies (Raun et al., 1998), and 0.1-1 mg/kg/day subcutaneously for chronic dosing studies in bone-metabolism and IGF-1 axis research (Svensson et al., 2000). In dogs and minipigs, comparable microgram/kg ranges have been reported. These ranges are provided strictly as references to the rodent and large-animal preclinical literature and are not recommendations for human use; ipamorelin research material sold by Viking Labs is for laboratory research only.

Handling, Reconstitution, and Storage

Lyophilized ipamorelin is generally stable at -20 degrees C protected from light for 24+ months. Once reconstituted in sterile bacteriostatic water (typical working concentration 1-2 mg/mL), the peptide should be refrigerated at 2-8 degrees C and used within approximately 14-30 days based on buffer and aseptic conditions. The peptide's small size and amidated C-terminus contribute to good solution stability relative to many larger peptides, but as with all GHS-class peptides, exposure to repeated freeze-thaw cycles or elevated temperatures should be avoided. See our peptide storage and stability reference.

HPLC Purity and Lab Specifications

• HPLC purity: greater than or equal to 98.0% (RP-HPLC, 214 nm)
• Identity: ESI-MS or MALDI-TOF; theoretical [M+H]+ approximately 712.9 Da
• Counterion content (typically acetate) reported on COA
• Endotoxin: less than 5 EU/mg
• Water content: typically less than 5% by Karl Fischer titration

For COA interpretation guidance, see How to read a peptide COA.

Cross-References --- Related Viking Labs Research

• Ipamorelin / CJC-1295 blend overview
• Growth hormone axis
• Ipamorelin ghrelin mimetic
• MOTS-c mitochondrial peptide overview
• Peptide reconstitution guide
• Understanding peptide purity
• WADA prohibited list 2026

*Provided for laboratory research purposes only. Not for human or veterinary use.*