Ghrelin receptor (GHSR-1a) agonist — selective GH secretagogue
Ipamorelin
Aib-His-D-2-Nal-D-Phe-Lys-NH2 — selective GHSR-1a (ghrelin receptor) agonist
Overview
Ipamorelin is a design story more than a discovery story. In the mid-1990s, researchers at Novo Nordisk set out to solve a specific pharmacologic problem: the existing GH-releasing peptides — GHRP-2, GHRP-6, hexarelin — all activated the ghrelin receptor GHSR-1a, but they also activated ACTH/cortisol and prolactin axes at the same doses. Cortisol elevation is exactly what you do not want from a growth-hormone-focused drug. The design brief was explicit — activate GHSR-1a for GH release, leave the other axes alone.
The result is astonishingly small. Five amino acids — Aib-His-D-2-Nal-D-Phe-Lys-NH2 — with two non-natural residues that give the pentapeptide receptor selectivity and metabolic stability. Raun EJE 1998 characterised the compound as 'the first selective growth hormone secretagogue' and the phrase has stuck. At doses that produce meaningful GH release, ACTH and cortisol stay at baseline and prolactin barely moves. This is what 'selective' means for ipamorelin.
The selectivity narrative deserves a caveat: it is dose-dependent. At higher doses, the selectivity window narrows — cortisol elevation appears in some studies once GHSR-1a activation saturates. So 'selective' is not an absolute property; it is a property of ipamorelin at doses that produce physiologic GH pulses. That's the operational reality, and it is why the human trials that exist (Gobburu 1999 PK/PD, Beck 2014 phase 2) stayed in careful dose ranges.
Quick Facts & Evidence
- Category
- Ghrelin receptor (GHSR-1a) agonist — selective GH secretagogue
- Research area
- GHSR agonist / GH secretagogue
- Most studied for
- GH-axis pharmacology research
- Combined GHRH + GHSR pulse-amplification research (with CJC-1295 No DAC)
- Post-operative ileus (phase-2 trial did not meet primary endpoint — Beck 2014)
- Age-related GH decline (preclinical / small studies)
- Clinical status
- Research use only — no approved clinical indication
- Human evidence
- Moderate Human Evidence
- Regulatory status
- Not approved by FDA, EMA or MHRA
Moderate Human Evidence
Supported by human trials, but of limited size, duration, or replication. May be approved for related but not identical indications.
Research Protocols
Research Protocol Snapshot
Preparation covered on this page
Freeze-dried injectable research format
This page covers the RUO lyophilized ipamorelin vial reconstituted with bacteriostatic water for subcutaneous research use, following the standard Healthy Mango preparation convention.
Ipamorelin research values at a glance.
| Item | Example value |
|---|---|
| Vial size | 10 mg |
| Liquid used to mix | Bacteriostatic water |
| Amount of liquid added | 2.0 mL |
| Final concentration | 5 mg/mL |
| How it's given | Subcutaneous injection |
| Research dose | 0.1–0.3 mg (100–300 mcg) per pulse |
| Frequency | 5×/week, fasted, pre-sleep |
| After mixing | Refrigerate; use within 7–10 days |
Reported Dosing
The practitioner-reference research protocol for ipamorelin is 0.1–0.3 mg per subcutaneous pulse, 5×/week, fasted, pre-sleep, across a 3-month cycle. It is educational reference, not a recommendation.
The Reported Protocol
| Dose | Frequency | Duration | Notes |
|---|---|---|---|
| 0.1–0.3 mg | 5×/week, fasted, pre-sleep, subcutaneous | 3 months on / 1 month off | 0.02–0.06 mL at 5 mg/mL |
Why protocols vary
The subcutaneous 0.1–0.3 mg per pulse range, dosed 5×/week fasted pre-sleep, is the practitioner-reference protocol for research contexts. It lines up with the Gobburu 1999 PK/PD dose-response in healthy volunteers.
The Beck 2014 phase-2 trial in post-operative ileus used higher intravenous doses (0.03 or 0.1 mg/kg three times daily) — that acute-care regimen is characteristic of the specific surgical indication and did not meet its primary endpoint, and is not what the subcutaneous research reference describes.
Preparing the Solution
Turning the freeze-dried powder into a measurable liquid.
Documented preparation
The documented research protocol is based on this preparation concentration.
Freeze-dried powder: 10 mg vial
Diluent: 2.0 mL bacteriostatic water
Final concentration: 5 mg/mL
Vial and volume from the practitioner reference; concentration calculated · Research-practitioner guide
Your vial
Matching preparation
Bacteriostatic water
2mL
Resulting concentration
5 mg/mL
Equivalent volume
The reported research amount of 0.10–0.30 mg is contained within
0.02–0.06mL
of the prepared solution now in your vial.
Show calculation
- Documented concentration
- 10 mg ÷ 2 mL = 5 mg/mL
- Bacteriostatic water to match the documented concentration
- 10 mg ÷ 5 mg/mL = 2 mL
- Equivalent volume at this concentration
- 0.10–0.30 mg ÷ 5 mg/mL = 0.02–0.06 mL
This tool performs arithmetic conversions using the preparation example and reported research amount shown on this page. It does not recommend an amount, route, preparation method, or use.
This tool performs arithmetic conversions using the preparation example and reported research amount shown on this page. It does not recommend an amount, route, preparation method, or use.Sources for these values
- Documented in the practitioner referenceResearch-practitioner guide
This example explains how concentration and volume are calculated for the standard RUO preparation. It is not a preparation guide.
How It's Given
Method used for this format
Subcutaneous injection, 5×/week fasted pre-sleep
Documented in the practitioner reference; Gobburu 1999 · Developer-authored review
Why this method
Ipamorelin is a five-amino-acid peptide; the subcutaneous route delivers it into circulation without the gastrointestinal degradation that would break the molecule down.
Pre-sleep timing aligns the pharmacologic pulse with the body's own overnight GH release; fasted timing avoids carbohydrate blunting of the same pulse. Both are consistent with the ~2-hour plasma half-life characterised in Gobburu 1999 and the pulsatile GH-release pharmacology ipamorelin was designed to mimic.
Injection sites reported
- Abdomen (rotate sites)
- Front of the thigh
- Avoid scarred, bruised, inflamed, or infected skin
Storage
Before mixing
- Refrigerate 2–8 °C
- Protect from light
- Do not freeze
Documented in the practitioner reference; general RUO practice · Research-practitioner guide
After mixing
- Refrigerate 2–8 °C
- Use within 7–10 days
- Do not freeze
- Discard if cloudy or discoloured
Documented in the practitioner reference · Research-practitioner guide
Handling
- Direct diluent slowly down the vial wall
- Gently swirl until dissolved — do not shake
- New sterile needle each draw
- Do not share vials
General RUO practice · Research-practitioner guide
Storage guidance summarises documented practitioner practice and standard RUO peptide handling. Verify the specific vial's supplied instructions before use.
Common Cycle
The practitioner-reference cadence is a 3-month active cycle followed by a 1-month washout — a duration chosen to prevent pituitary desensitisation.
- Cycle Length
- 3 months on
- Break Before the Next Cycle
- 1-month washout between cycles
- What the Research Shows
- Not defined (no phase-3 program)
Documented in the practitioner reference · Research-practitioner guide
The Gobburu 1999 study characterised the ~2 h plasma half-life in single-dose administration; the Beck 2014 phase-2 trial in post-operative ileus tested a much shorter intensive IV course. Neither is the on/off cycle the practitioner reference describes.
Compound Overview
Current areas of research
There is no approved indication for ipamorelin. The following are effects reported in preclinical or research contexts.
- Selective GH release via GHSR-1a activation without ACTH/cortisol or prolactin elevation at active doses (Raun 1998)
- Additive GH pulse when paired with a GHRH analogue in research protocols
- Preclinical models suggest a role in age-related GH decline (small studies)
- Investigational phase-2 use in post-operative ileus did not meet primary endpoint (Beck 2014) but characterised safety
Mechanism of action
Ipamorelin is a design story more than a discovery story. In the mid-1990s, researchers at Novo Nordisk set out to solve a specific pharmacologic problem: the existing GH-releasing peptides — GHRP-2, GHRP-6, hexarelin — all activated the ghrelin receptor GHSR-1a, but they also activated ACTH/cortisol and prolactin axes at the same doses. Cortisol elevation is exactly what you do not want from a growth-hormone-focused drug. The design brief was explicit — activate GHSR-1a for GH release, leave the other axes alone.
The result is astonishingly small. Five amino acids — Aib-His-D-2-Nal-D-Phe-Lys-NH2 — with two non-natural residues that give the pentapeptide receptor selectivity and metabolic stability. Raun EJE 1998 characterised the compound as 'the first selective growth hormone secretagogue' and the phrase has stuck. At doses that produce meaningful GH release, ACTH and cortisol stay at baseline and prolactin barely moves. This is what 'selective' means for ipamorelin.
The selectivity narrative deserves a caveat: it is dose-dependent. At higher doses, the selectivity window narrows — cortisol elevation appears in some studies once GHSR-1a activation saturates. So 'selective' is not an absolute property; it is a property of ipamorelin at doses that produce physiologic GH pulses. That's the operational reality, and it is why the human trials that exist (Gobburu 1999 PK/PD, Beck 2014 phase 2) stayed in careful dose ranges.
- Deliberately designed at Novo Nordisk — not a natural GHSR ligand, but a five-amino-acid peptide engineered for receptor selectivity
- 'First selective GH secretagogue' (Raun 1998) — active GH-releasing doses do not elevate cortisol or prolactin; selectivity narrows at higher doses
- The Beck 2014 phase-2 trial in post-operative ileus did not meet its primary endpoint — a result about that specific surgical indication, not about the compound itself
Human research
The published evidence base is small but coherent. Raun EJE 1998 is the foundational paper — the demonstration that a rationally designed pentapeptide could release GH via GHSR-1a without triggering the cortisol/prolactin axes that made older GH-releasing peptides poorly suited for endocrine research. Andersen GHIR 2001 followed with additional preclinical characterisation, extending the selectivity findings to different animal models. Both are Level-C animal evidence, but they are direct evidence about this molecule.
Human evidence comes from two sources. Gobburu Pharm Res 1999 provides the fundamental PK/PD characterisation in healthy volunteers — the ~2-hour half-life, the ascending-dose GH-release relationship, and confirmation that the selectivity observed in animals translates to humans at the tested doses. Beck IJCD 2014 is the phase-2 randomised trial in post-operative ileus that did not meet its primary endpoint but characterised safety in a post-surgical population.
Evidence level is Level B (moderate). The design intent is well established, the mechanism is well characterised, and the compound has human safety data. What is missing is a modern controlled trial in an indication where the mechanism actually fits — which is a comment about the development program that never happened, not a comment about the compound itself.
Raun EJE 1998
Discovery and preclinical characterisation of ipamorelin. Established selectivity at GHSR-1a: GH release without cortisol or prolactin activation at active doses — the pharmacologic feature that distinguishes ipamorelin from older GH-releasing peptides.
Gobburu Pharm Res 1999
PK/PD modelling of ipamorelin in human volunteers. Established the ~2-hour half-life and GH-release dose-response, providing the human pharmacology foundation for the compound.
Beck IJCD 2014
Phase-2 randomised, double-blind, placebo-controlled trial of ipamorelin in post-operative ileus after bowel resection. Did not meet the primary endpoint (time to recovery of upper and lower GI function). Characterised safety in a surgical population.
Andersen GHIR 2001
Preclinical characterisation of ipamorelin as a novel and selective GH secretagogue. Additional support for the receptor-level selectivity described in Raun 1998.
Beck 2014 is worth understanding on its own terms, because it is often summarised as 'the ipamorelin trial failed' — which is technically true and substantively misleading. The trial tested whether ipamorelin at 0.03 or 0.1 mg/kg three times daily could shorten time to recovery of upper and lower gastrointestinal function after bowel resection surgery. That endpoint (a composite of first tolerated diet, first flatus, and first bowel movement) is influenced by pain-medication regimens, surgical technique, patient comorbidities, and post-operative care in ways that do not map cleanly onto what a GH secretagogue actually does. The endpoint's fit to the drug's mechanism was arguably weak.
The trial did establish that ipamorelin is safe in a post-surgical population at the tested doses, and it characterised the human dose-response in a way that Gobburu 1999's smaller PK study could not. Those are useful contributions. They are not, however, contributions that justify a phase-3 program for post-operative ileus, and Helsinn's program ended there.
The result is that ipamorelin sits in an unusual regulatory position: a compound with human safety data, a well-characterised mechanism, published pharmacokinetics, and no active development program under any brand or sponsor. Access is via compounding pharmacies (where legally permitted) or research-supply channels. There is no post-marketing surveillance dataset, because there is no marketing.
Safety considerations
The following have been reported in the Gobburu 1999 and Beck 2014 human trials and in preclinical studies.
- Injection-site reactions
- Headache — Transient
- Nausea — Dose-related, reported at higher IV doses in Beck 2014
- Water retention — Especially with sustained daily use
- Elevated IGF-1 — With prolonged use; monitor
- Increased appetite is possible — GHSR-1a is the endogenous ghrelin receptor and mediates appetite
- Rare: hypersensitivity
There is no approved-label list of contraindications because there is no approved indication. The following draws on the general GH-secretagogue safety class and the Beck 2014 trial safety data.
- Disruption of the hypothalamic-pituitary axis (hypophysectomy, hypopituitarism, pituitary tumour surgery, head irradiation, head trauma)
- Active malignancy (theoretical risk from IGF-1 elevation)
- Pregnancy
- Known hypersensitivity to GH secretagogues
- Not appropriate for concurrent use with rhGH replacement
Monitoring
- IGF-1 (baseline and periodic if used long-term in research)
- Fasting glucose and HbA1c in participants with diabetes or prediabetes
- Injection-site reactions across rotation sites
- Signs of fluid retention
Frequently asked questions
Is ipamorelin actually selective at every dose?
No — and this is a nuance most sources gloss over. Ipamorelin's selectivity for GH release over cortisol and prolactin is a property of doses that produce physiologic GH pulses. At higher doses, the selectivity window narrows and cortisol elevation appears in some studies. So the accurate framing is: at active doses, ipamorelin releases GH without activating the ACTH/cortisol or prolactin axes. That's a meaningful distinction from GHRP-2 or GHRP-6, but 'selective' should not be read as an absolute property independent of dose.
Why is the peptide only five amino acids long?
Because Novo Nordisk designed it to be the minimum sequence that would achieve the selectivity goal. Aib (α-aminoisobutyric acid) at position 1 gives metabolic stability; D-2-Nal at position 3 is essential for GHSR-1a binding; D-Phe at position 4 adds selectivity. The two natural residues (histidine, lysine) round out the structure. The five-amino-acid length isn't a coincidence — it's the result of a systematic reduction from longer parent peptides.
What actually happened with Beck 2014?
The trial tested ipamorelin at 0.03 or 0.1 mg/kg three times daily against placebo in patients recovering from bowel resection surgery. The primary endpoint was time to recovery of upper and lower GI function (a composite of first tolerated diet, first flatus, first bowel movement). Ipamorelin did not produce a statistically significant improvement. The result speaks specifically to that composite endpoint in that specific surgical population; it does not speak to the underlying pharmacology, which was well characterised in Gobburu 1999. The mechanism didn't fail — the indication was arguably a poor fit for a GH secretagogue.
Why is it always paired with CJC-1295 No DAC in research?
The pharmacologic rationale is receptor-level additivity. Both compounds trigger GH release from the same pituitary somatotrophs, but through different receptors — ipamorelin via GHSR-1a, CJC-1295 No DAC via GHRH-R. The two signals converge on the same intracellular machinery and produce a larger combined GH pulse than either compound alone. That's the empirical finding; the research-community protocol convention (co-administration) follows the mechanism.
Does ipamorelin make people hungry?
GHSR-1a is the endogenous ghrelin receptor, and endogenous ghrelin is a hunger hormone. So the biology says yes — some appetite stimulation should be expected. In practice, research reports of appetite change with ipamorelin are milder than with endogenous ghrelin, likely because the peptide's engagement of the receptor is designed around GH release rather than hypothalamic feeding circuits. Individual responses vary, and the effect has not been systematically characterised across dose ranges.
References
- [1]
Ipamorelin, the first selective growth hormone secretagogue — Raun K, Hansen BS, Johansen NL, et al., European Journal of Endocrinology (1998)
- [2]
Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers — Gobburu JVS, Agersø H, Jusko WJ, Ynddal L, Pharmaceutical Research (1999)
- [3]
Ipamorelin, a growth hormone secretagogue, does not reduce postoperative ileus in patients undergoing bowel resection: results of a phase 2, randomized, double-blind, placebo-controlled trial — Beck DE, Sweeney WB, McCarter MD, Ipamorelin 2201 Study Group, International Journal of Colorectal Disease (2014)
- [4]
Ipamorelin, a novel and selective growth hormone secretagogue: preclinical characterization — Andersen NB, Malmlöf K, Johansen PB, Andreassen TT, Ørtoft G, Oxlund H, Growth Hormone & IGF Research (2001)
- [5]
Peptides & Compounds — The No-Jargon Guide (v5) — Healthy Mango Editorial, Healthy Mango practitioner reference (2026)
Laboratory Reference Notice
This section summarizes procedures and study parameters reported in published scientific literature and laboratory protocols. It is provided for educational and research reference only and must not be interpreted as medical advice, clinical guidance, or instructions for personal use.
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