# Ipamorelin — Research Peptide Profile

> Ipamorelin raises GH without cortisol or prolactin spikes — a selectivity unique among GHRPs. Human PK data, research dosing, half-life, safety profile & cited studies.

Source: https://peptpedia.org/peptide/ipamorelin | Published: 2025-12-02 | Last updated: 2026-08-04 | Medically reviewed: 2025-12-27

Ipamorelin is a pentapeptide growth hormone secretagogue that stimulates the pituitary via the ghrelin receptor. It stands apart from older GHRPs for selectivity: in human studies it raised GH without meaningfully elevating cortisol or prolactin. Human data is limited to a handful of trials, and its development program ended before approval.

## Overview

Ipamorelin is a synthetic pentapeptide growth hormone secretagogue that acts as a selective agonist at the [ghrelin receptor (GHSR-1a)](/research/ipamorelin-ghs-pathway). First described by Raun et al. in 1998, it is distinguished from other GHRPs by releasing GH without meaningfully elevating cortisol, prolactin, or ACTH at therapeutic doses—a selectivity profile unique among its class. Human data is limited to two PK/PD studies and a discontinued Phase II trial; the majority of evidence derives from rodent models.

## Molecular Profile

- **Category:** growth-factors
- **Molecular formula:** C38H49N9O5
- **Molecular weight:** 711.85 g/mol
- **CAS number:** 170851-70-4
- **Amino acid sequence:** Aib-His-D-2-Nal-D-Phe-Lys-NH2
- **Also known as:** Ipamorelin Acetate, NNC 26-0161
- **Half-life:** Approximately 2 hours
- **Solubility:** Soluble in water and bacteriostatic water
- **Storage:** Store lyophilized peptide at -20°C. Reconstituted solution at 2-8°C.

## Mechanism of Action

Ipamorelin acts as an agonist at the ghrelin receptor (GHSR-1a) in the pituitary gland, stimulating the release of growth hormone through activation of specific signaling pathways (PMID: 9849822). It mimics the action of the natural hormone ghrelin but with higher selectivity. The peptide stimulates GH release in a dose-dependent manner while maintaining the natural pulsatile pattern of GH secretion. Importantly, it does not significantly stimulate ACTH, cortisol, or prolactin release at physiological doses (PMID: 9849822).

## Key Research Findings

- Ipamorelin is called the first truly selective growth hormone secretagogue because it stimulates GH release without measurably raising cortisol, prolactin, or ACTH at therapeutic doses.
- Unlike most GHRPs, Ipamorelin preserves the natural pulsatile rhythm of growth hormone release rather than forcing a continuous elevation, maintaining normal feedback regulation.
- Ipamorelin has only a handful of human studies, primarily pharmacokinetic trials and a discontinued Phase II for postoperative ileus, making its widespread popularity largely based on animal data.
- In glucocorticoid-treated rats mimicking osteoporosis, Ipamorelin counteracted steroid-induced bone loss by enhancing bone formation without changing bone mineral density markers.

## Selective Somatotroph Activation: The Clean GH Release Profile

Ipamorelin's pharmacokinetic profile reflects its design as a selective growth hormone secretagogue — achieving rapid, pulsatile GH release without the off-target hormonal effects that limit other GHRPs. Its short half-life is a feature, not a limitation, preserving the physiologic pulsatility of GH secretion.

### Rapid Absorption and GH Pulse Kinetics

Following subcutaneous administration, ipamorelin produces a discrete GH pulse that mimics the amplitude and duration of endogenous GH secretory episodes.

- Subcutaneous Tmax is 15-30 minutes, with peak plasma ipamorelin concentrations followed by a terminal elimination half-life of approximately 2 hours.
- GH release begins within 10 minutes of administration, peaks at 30-40 minutes, and returns to baseline by approximately 3 hours — producing a single, clean GH pulse per dose.
- No accumulation occurs with repeated dosing. Each injection produces an independent GH secretory episode, preserving the pulsatile pattern that maintains GH receptor sensitivity.

### The Selectivity Advantage: What Ipamorelin Does NOT Release

Ipamorelin's defining pharmacological feature is not what it stimulates but what it does not — a selectivity profile that distinguishes it from earlier growth hormone secretagogues.

- Unlike GHRP-6 and GHRP-2, ipamorelin does not elevate plasma cortisol or ACTH at growth hormone-releasing doses. This avoids the catabolic and immunosuppressive effects of cortisol elevation.
- No significant prolactin elevation occurs, eliminating the gynecomastia concerns associated with GHRP-2 at higher doses.
- No ghrelin-mimetic appetite stimulation — unlike GHRP-6, which produces intense hunger within minutes of injection through direct ghrelin receptor activation in the hypothalamic arcuate nucleus.

## Safety & Tolerability

Ipamorelin's defining tolerability feature is selectivity: in its foundational pharmacology it stimulated growth-hormone release without meaningfully raising cortisol, prolactin, or ACTH, and without the appetite stimulation seen with other growth-hormone-releasing peptides — avoiding several of their characteristic side effects. Published human exposure is limited to pharmacokinetic/pharmacodynamic study and a completed Phase II trial; long-term human safety is not established.

**Human data status:** Human data comprises pharmacokinetic/pharmacodynamic study in volunteers and a completed Phase II trial for postoperative ileus (NCT00672074); ipamorelin's development for that indication was subsequently discontinued without approval, and no efficacy trials for growth-hormone deficiency, body composition, or anti-aging have been published. Long-term safety is uncharacterized.

**Regulatory status:** Not approved for human use by any regulatory agency; available only as a research compound.

- Ipamorelin stimulated GH release without significantly increasing cortisol, prolactin, or ACTH at GH-releasing doses, and without the appetite stimulation of GHRP-6 — a selectivity profile that avoids several side effects associated with earlier growth-hormone-releasing peptides. (evidence tier: animal; [PMID 9849822](https://pubmed.ncbi.nlm.nih.gov/9849822/))
- Ipamorelin advanced to a completed Phase II clinical trial for postoperative ileus (NCT00672074); its clinical development for that indication was later discontinued without regulatory approval. (evidence tier: human-interventional)

## Dosing Information (Research Context)

Research protocols have utilized dosages ranging from 1 mcg/kg to 3 mcg/kg, typically administered subcutaneously. Note: Ipamorelin has very limited human clinical data (primarily two PK/PD studies and a discontinued Phase II trial for postoperative ileus). Animal studies have used various dosing regimens depending on the research objectives (PMID: 11735244, PMID: 10828840). Most research protocols involve administration 1-3 times daily to mimic natural GH pulsatility.

| Route | Dose | Frequency | Notes |
| --- | --- | --- | --- |
| Subcutaneous | 1–3 mcg/kg | 1–3× daily | Mimics pulsatile GH secretion; most studied route |
| Intravenous | 1–3 mcg/kg | Single dose | Used in PK/PD studies (PMID: 10496658) |
| Intraperitoneal | 1–3 mcg/kg | Daily | Rodent bone and metabolic studies |

## Researched Effects

- **Growth Hormone Release** (evidence: moderate): Research demonstrates significant, dose-dependent increases in growth hormone levels following Ipamorelin administration (PMID: 9849822), with peak GH concentrations occurring approximately 30-40 minutes post-injection (PMID: 10496658). Studies consistently show that Ipamorelin maintains the natural pulsatile pattern of GH secretion rather than causing unnatural sustained elevation, which is considered beneficial for maintaining normal feedback regulation (PMID: 9849822). While Ipamorelin's human data is limited (primarily PK/PD studies and a discontinued Phase II for postoperative ileus), the dose-dependent acute stimulation aligns with 3-10 fold increases in peak GH, with effects lasting approximately 2-3 hours per administration (PMID: 10496658). The peptide has been studied for optimization of natural GH production patterns (PMID: 9849822), though it has not been extensively studied for age-related hormone decline or adult growth hormone deficiency in clinical trials.
- **Selective GH Stimulation** (evidence: extensive): One of Ipamorelin's most significant research advantages is its remarkable selectivity for growth hormone release without substantial effects on other pituitary hormones or stress hormones. Clinical studies demonstrate minimal impact on cortisol levels (unlike GHRP-6 and GHRP-2), negligible prolactin elevation, and no significant effects on FSH, LH, TSH, or ACTH at therapeutic dosages. This selectivity profile makes Ipamorelin invaluable for research requiring isolated study of GH pathway effects without confounding hormonal variables. The peptide's clean hormonal profile has made it the preferred GHRP for many endocrinology research applications studying GH deficiency, aging, and metabolic regulation.
- **Body Composition Effects** (evidence: moderate): Research in animal models and preliminary human studies indicates Ipamorelin may influence body composition through GH-mediated pathways including enhanced lipolysis (fat breakdown), increased lean body mass, and improved fat-free mass to fat mass ratios. Studies have documented potential effects on visceral adipose tissue (belly fat), subcutaneous fat distribution, and skeletal muscle protein synthesis. The peptide has been investigated for applications in obesity research, sarcopenia (age-related muscle loss) studies, and metabolic syndrome investigations. Long-term administration studies in animals suggest sustained improvements in body composition metrics without significant adverse effects.
- **Bone Density Research** (evidence: preliminary): Studies suggest Ipamorelin may positively influence bone metabolism through mechanisms involving growth hormone and IGF-1 elevation (PMID: 9849822, PMID: 10373343). While GH and IGF-1 positively influence bone metabolism, the direct effect of Ipamorelin on bones is less studied. Research in animal models has documented increased longitudinal bone growth in young subjects (PMID: 10373343) and increased bone mineral content (BMC) due to increased volume of bone, though bone mineral density itself remained unchanged (PMID: 10828840). Note: No significant changes in bone turnover markers (osteocalcin and bone-specific alkaline phosphatase) were observed in studies (PMID: 10373343, PMID: 10828840). The peptide was studied in an osteoporosis-mimicking model (glucocorticoid-induced bone loss in adult rats), where it enhanced bone formation (PMID: 11735244). Studies show Ipamorelin causes pulsatile GH release (not sustained elevation), indicating it may preserve normal feedback regulation while potentially supporting bone remodeling processes.
- **Sleep and Recovery Research** (evidence: preliminary): The relationship between growth hormone secretion and sleep quality is well-established in endocrinology research, as natural GH release peaks during slow-wave (deep) sleep. Since Ipamorelin stimulates pulsatile GH release that mimics natural patterns (PMID: 9849822), researchers have hypothesized potential benefits for sleep architecture. However, direct studies specifically evaluating Ipamorelin's effects on sleep quality metrics are limited. Any observed sleep-related effects would theoretically be mediated through GH pathway activation rather than direct CNS effects. Further research is needed to establish whether Ipamorelin administration influences sleep architecture, recovery processes, or subjective sleep quality in controlled settings.

## Research Applications

- Endocrinology
- Metabolism Research
- Aging Studies
- Body Composition Research
- Bone Health Research

## Key Studies

### Ipamorelin, the first selective growth hormone secretagogue

Raun K, Hansen BS, Johansen NL, et al. — *European Journal of Endocrinology* (1998) — [PMID 9849822](https://pubmed.ncbi.nlm.nih.gov/9849822/) | [doi:10.1530/eje.0.1390552](https://doi.org/10.1530/eje.0.1390552)

This foundational study established Ipamorelin as a selective growth hormone secretagogue, demonstrating its unique ability to stimulate GH release without significantly affecting cortisol, prolactin, or ACTH levels. The research showed dose-dependent GH release while maintaining natural pulsatile secretion patterns. This selectivity profile distinguished Ipamorelin from earlier GHRPs like GHRP-6 and GHRP-2, establishing it as a valuable tool for isolated GH research.

### Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers

Gobburu JV, Agersø H, Jusko WJ, Ynddal L — *Pharmaceutical Research* (1999) — [PMID 10496658](https://pubmed.ncbi.nlm.nih.gov/10496658/) | [doi:10.1023/a:1018955126402](https://doi.org/10.1023/a:1018955126402)

This PK/PD study in human volunteers documented Ipamorelin's pharmacokinetic profile, showing peak GH concentrations approximately 30-40 minutes post-injection with effects lasting 2-3 hours. The research established dose-response relationships and confirmed the peptide's favorable pharmacological characteristics for GH research applications.

### Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats

Johansen PB, Nowak J, Skjaerbaek C, et al. — *Growth Hormone & IGF Research* (1999) — [PMID 10373343](https://pubmed.ncbi.nlm.nih.gov/10373343/) | [doi:10.1054/ghir.1999.9998](https://doi.org/10.1054/ghir.1999.9998)

This study demonstrated Ipamorelin's effects on longitudinal bone growth in rat models. Researchers documented increased tibial bone length through GH-mediated mechanisms. Notably, no significant changes in bone turnover markers (osteocalcin, bone-specific alkaline phosphatase) were observed, indicating effects primarily through bone volume rather than remodeling markers.

### The GH secretagogue ipamorelin counteracts glucocorticoid-induced decrease in bone formation of adult rats

Andersen NB, Malmlöf K, Johansen PB, et al. — *Growth Hormone & IGF Research* (2001) — [PMID 11735244](https://pubmed.ncbi.nlm.nih.gov/11735244/) | [doi:10.1054/ghir.2001.0239](https://doi.org/10.1054/ghir.2001.0239)

This study investigated Ipamorelin in a glucocorticoid-induced bone loss model (mimicking osteoporosis conditions). Results showed Ipamorelin enhanced bone formation in adult rats treated with dexamethasone, suggesting potential applications in studying GH-based interventions for steroid-induced bone loss.

## Frequently Asked Questions

### What makes Ipamorelin selective compared to other GHRPs?

Unlike GHRP-6 and GHRP-2, Ipamorelin stimulates GH release without meaningfully elevating cortisol, prolactin, or ACTH at physiological doses (PMID: 9849822). This is because Ipamorelin has high selectivity for the GHSR-1a receptor on pituitary somatotrophs and does not significantly activate the adrenocortical axis or stimulate prolactin-releasing pathways. It also lacks the potent ghrelin-mimetic appetite-stimulating effects seen with GHRP-6, making it cleaner for isolated GH research.

### What human clinical data exists for Ipamorelin?

Ipamorelin's human data is limited to two published pharmacokinetic/pharmacodynamic studies: a 1999 PK/PD study (PMID: 10496658) that documented dose-response relationships and peak GH at 30-40 minutes post-injection in human volunteers, and a completed Phase II clinical trial for postoperative ileus (NCT00672074), after which ipamorelin's development for this indication was discontinued without approval. No published human efficacy trials for GH deficiency, body composition, or anti-aging applications exist. The extensive preclinical literature should not be conflated with established human clinical efficacy.

### How does Ipamorelin preserve the natural pulsatility of GH secretion?

Ipamorelin stimulates GH release in discrete pulses that clear from circulation relatively quickly (plasma half-life approximately 2 hours), allowing the pituitary to return to baseline between doses. This mirrors the natural pattern of GH secretion, which occurs in 4-6 pulses per day—predominantly during deep sleep. Continuous GH elevation (as with exogenous GH administration) suppresses this natural pulsatility and can downregulate GH receptors. Ipamorelin's pulsatile profile may better preserve normal GH axis feedback compared to sustained-release compounds.

### How does Ipamorelin compare to CJC-1295?

They work through complementary but different mechanisms. Ipamorelin activates the ghrelin receptor (GHSR-1a), while CJC-1295 activates the GHRH receptor on the same pituitary somatotroph cells. Because these are separate receptor systems, the combination produces synergistic GH release greater than either alone. CJC-1295 (with DAC) provides sustained background GH elevation lasting days, while Ipamorelin creates acute GH pulses. The combination protocol exploits both pathways simultaneously to maximize GH output.

### What bone research has been done with Ipamorelin?

Ipamorelin has been studied in two bone-related rodent models. A 1999 study (PMID: 10373343) showed increased longitudinal bone growth (tibial length) with no significant change in bone turnover markers (osteocalcin, BSAP)—suggesting growth through increased bone volume rather than remodeling. A 2001 study (PMID: 11735244) found Ipamorelin partly counteracted glucocorticoid-induced bone formation loss in adult rats. These findings suggest bone-supportive effects mediated through GH/IGF-1 but do not establish clinical efficacy for osteoporosis prevention.

### Can Ipamorelin be combined with other peptides?

In research settings, Ipamorelin is frequently studied in combination with GHRH analogs like CJC-1295 or Sermorelin. The synergistic effect arises because the two receptor pathways (GHSR-1a for Ipamorelin, GHRHR for the GHRH analog) amplify each other's pituitary stimulation. This combination has been shown to produce 2-5× greater GH release than either compound alone. Combinations with other peptides have not been formally studied in published clinical research.

### What is the half-life of Ipamorelin?

Human pharmacokinetic data from the 1999 PK/PD study (PMID: 10496658) documented a plasma half-life of approximately 2 hours in humans. Peak GH concentrations occurred 30-40 minutes post-subcutaneous injection, with GH effects persisting 2-3 hours. The relatively short half-life supports multi-daily dosing protocols designed to create GH pulses that mimic the natural circadian pattern of growth hormone secretion.

### What side effects have been observed with Ipamorelin in research?

In published human PK/PD studies, Ipamorelin demonstrated a favorable tolerability profile. Unlike GHRP-6, it does not significantly stimulate appetite (minimal ghrelin-mimetic effects at the hypothalamic level). Unlike GHRP-2, it does not significantly elevate cortisol or ACTH. Common mild observations in studies include transient facial flushing and headache. No serious adverse events specific to Ipamorelin were documented in the limited published human data. The long-term safety profile in humans is not established due to the absence of extended clinical trials.

### What is the rationale for combining Ipamorelin with CJC-1295?

Ipamorelin (GHRP, activates GHSR-1a on somatotrophs) and CJC-1295 (GHRH analog, activates GHRHR on somatotrophs) stimulate growth hormone release through two complementary receptor pathways on the same pituitary cell type. When administered together, the GH response is synergistic — typically 2-5 times greater than either peptide alone — because GHRH primes the somatotroph's secretory capacity while GHRP triggers the actual GH release burst. This combination protocol has become the standard in GH research.

### When is the optimal time to administer Ipamorelin in research settings?

Administration before sleep is most common in research protocols, timed to coincide with the natural nocturnal GH surge that occurs during slow-wave sleep. The peptide should be administered in a fasting state — food intake, particularly carbohydrates and fats, blunts the GH response by up to 50% through elevations in insulin, free fatty acids, and somatostatin. A minimum 2-hour fast before administration is the standard protocol.

### Why does Ipamorelin's selectivity matter compared to other growth hormone secretagogues?

Ipamorelin's selectivity means it stimulates GH release without the unwanted hormonal side effects of earlier GHRPs. GHRP-6 produces intense hunger (through direct ghrelin receptor activation) and elevates cortisol. GHRP-2 is more potent for GH release but also elevates prolactin at higher doses, raising gynecomastia concerns. Hexarelin is the most potent GHRP but desensitizes rapidly with repeated dosing. Ipamorelin avoids all of these issues — no cortisol, no prolactin, no appetite surge, no rapid desensitization — making it the preferred research GHRP for protocols requiring clean GH data.

### How does Ipamorelin compare to exogenous growth hormone injection?

Exogenous GH (recombinant hGH) provides a direct, supraphysiologic GH bolus that bypasses the pituitary entirely. Ipamorelin stimulates the pituitary to release endogenous GH, preserving the natural pulsatile secretion pattern. Key differences: exogenous GH suppresses endogenous GH production through negative feedback (IGF-1 → hypothalamus), while ipamorelin does not. Exogenous GH produces higher absolute GH levels but at the cost of receptor desensitization with chronic use. Ipamorelin produces lower peak GH concentrations but maintains pituitary axis integrity.

### Does Ipamorelin increase cortisol or prolactin?

No — this selectivity is Ipamorelin's defining feature. In its foundational selectivity study (PMID: 9849822), Ipamorelin stimulated GH release without meaningfully elevating cortisol, ACTH, or prolactin at GH-releasing doses — a selectivity profile unique among GHRPs. This distinguishes it from GHRP-6, which elevates cortisol and stimulates appetite, and from GHRP-2, which elevates prolactin at higher doses. The clean hormonal profile is why Ipamorelin became the preferred GHRP for research requiring isolated GH pathway effects.

## Related Peptides

- [CJC-1295](https://peptpedia.org/peptide/cjc-1295)
- [GHRP-6](https://peptpedia.org/peptide/ghrp-6)
- [GHRP-2](https://peptpedia.org/peptide/ghrp-2)
- [Hexarelin](https://peptpedia.org/peptide/hexarelin)
- [IGF-1 LR3](https://peptpedia.org/peptide/igf-1-lr3)
- [MK-677 (Ibutamoren)](https://peptpedia.org/peptide/mk-677)

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