What is ipamorelin?
Ipamorelin was characterised in 1998 by Raun and colleagues, who reported growth-hormone release in animal models with a selectivity profile that distinguished it from earlier secretagogues — notably a lack of the ACTH and cortisol elevation seen with some other compounds in that class. [1]
For the compound overview alongside CJC-1295, see what CJC-1295 and ipamorelin are.
How does ipamorelin work?
Ipamorelin binds the growth hormone secretagogue receptor (GHS-R), the receptor for ghrelin, on pituitary somatotrophs and elsewhere. Activation promotes growth-hormone release through a pathway distinct from GHRH receptor signalling.
The receptor-level detail is covered in the CJC-1295 and ipamorelin mechanism guide, which this page does not duplicate.
What early research studied ipamorelin?
The founding paper is animal pharmacology. Raun and colleagues reported dose-dependent growth-hormone release in rats and swine, and described ipamorelin as the first selective growth hormone secretagogue on the basis of its hormone-release profile. [1]
Evidence level: animal pharmacology. Potency values derived in rats and swine describe those species under those protocols and do not transfer directly to humans.
What human studies exist?
Two lines of human work are indexed.
The first is pharmacokinetic and pharmacodynamic. Gobburu and colleagues studied intravenous ipamorelin in healthy male volunteers using a dose-escalation design with five infusion rates (4.21, 14.02, 42.13, 84.27 and 140.45 nmol/kg over 15 minutes), with eight subjects at each dose level. [2]
| Study design | Detail |
|---|---|
| Design | Dose-escalation, five intravenous infusion rates over 15 minutes |
| Participants | Eight healthy male subjects at each dose level |
| Measured | Ipamorelin and growth-hormone concentrations |
| Endpoint | Result |
| Terminal half-life | Approximately 2 hours |
| Clearance | 0.078 L/h/kg; steady-state volume of distribution 0.22 L/kg |
| GH response | Single episode of release, peak at 0.67 hours, exponential decline at all doses |
| SC50 for half-maximal GH stimulation | 214 nmol/L |
Two points deserve emphasis. Ipamorelin produced a single pulse of growth hormone that decayed to negligible concentrations at every dose tested — not a sustained elevation. And inter-individual variability in the pharmacodynamic parameters was larger than in the pharmacokinetic ones. [2]
The second line is clinical. Ipamorelin was developed for postoperative ileus — delayed return of gut function after abdominal surgery — on the rationale that ghrelin-receptor stimulation has promotility effects. The proof-of-concept phase 2 trial was published in 2014. [3]
| Study design | Detail |
|---|---|
| Design | Multicentre, double-blind, placebo-controlled |
| Population | Adults undergoing small and large bowel resection, open or laparoscopic |
| Enrolment | 117 patients enrolled; 114 in the safety and modified intent-to-treat populations |
| Intervention | Intravenous ipamorelin 0.03 mg/kg twice daily versus placebo, postoperative day 1–7 or discharge |
| Registry | NCT00672074 |
| Endpoint | Result |
| Primary endpoint — median time to first tolerated solid meal | 25.3 h ipamorelin vs 32.6 h placebo (p = 0.15; not significant) |
| Treatment-emergent adverse events | 87.5% ipamorelin vs 94.8% placebo |
| Authors' conclusion | Well tolerated; no significant difference on key or secondary efficacy analyses |
The direction of the difference favoured ipamorelin, but the trial did not reach statistical significance and the authors reported it as negative on efficacy. The paper itself notes the study was small and enrolled patients with a broad range of underlying conditions. [3]
What did clinical development investigate?
The registry record fills in what publication does not.
The larger dose-finding trial, with 320 participants, completed in 2014. No results have been posted to the registry and no peer-reviewed publication of its results could be located. Development under that sponsor did not continue to a reported phase 3 programme.
Completed is not the same as reported. A trial that finished twelve years ago without posted results leaves a real gap in the evidence base, and that gap should be stated rather than filled with inference.
What did the evidence not demonstrate?
This list is as important as the findings.
- No human trial measured body composition, lean mass or fat mass as an endpoint.
- No human trial measured muscle strength or physical performance.
- No human trial examined ageing, longevity or recovery outcomes.
- The one published efficacy trial did not meet its primary endpoint. [3]
- Sustained elevation of growth hormone was not demonstrated; the human pharmacodynamic study described a single pulse decaying to negligible concentrations. [2]
Claims about body composition or anti-ageing effects therefore have no human ipamorelin trial behind them. They may be inferences from growth-hormone physiology generally, but an inference is not a finding, and this page does not present one as the other.
Has ipamorelin been studied together with CJC-1295?
No published human study of the combination could be located, and no registered trial of the two administered together appears in ClinicalTrials.gov.
The rationale offered for combining them is that a GHRH-receptor agonist and a ghrelin-receptor agonist act through different pathways, and that combined GHRH plus GHRP administration produced greater growth-hormone release than either alone in earlier human work with different molecules. [6] That is a reasonable hypothesis. It is not evidence about CJC-1295 with ipamorelin specifically.
The combination question is examined in more depth in the CJC-1295 and ipamorelin evidence review.
What remains unknown?
- The results of NCT01280344, the largest ipamorelin trial conducted, which completed in 2014 without posted results. [5]
- Whether repeated administration produces any sustained endocrine change, as opposed to repeated single pulses.
- Any effect on body composition or functional outcomes, which has never been tested in humans.
- Whether combination with a GHRH-receptor agonist produces additive or synergistic effects in humans.
- Long-term safety beyond the one-week postoperative exposure studied. [3]
Frequently Asked Questions
Is there human evidence for ipamorelin?
Yes, but it is limited: a dose-escalation pharmacokinetic study in healthy male volunteers, and two completed phase 2 trials in surgical patients, one of which was published and missed its primary endpoint.
Did ipamorelin work for postoperative ileus?
The published proof-of-concept trial reported a median time to first tolerated meal of 25.3 hours versus 32.6 hours for placebo, p = 0.15 — not statistically significant.
Has ipamorelin been tested with CJC-1295?
No published or registered human study of the two administered together could be located.
