Ipamorelin vs MK-677 (Ibutamoren)
Ipamorelin (Growth-hormone secretagogue (GHRP) / ghrelin receptor agonist) and MK-677 (Ibutamoren) (Orally active non-peptide growth-hormone secretagogue (ghrelin-receptor agonist)) are documented as co-studied in the PeptiDex library. This page puts the two entries side by side on class, molecular weight, half-life, origin, mechanism and studied research areas — every value taken from the entry it belongs to.
Why these two are co-studied
Cross-referenced for research context — not a usage or combination recommendation.
At a glance
| Attribute | Ipamorelin | MK-677 (Ibutamoren) |
|---|---|---|
| Compound class | Growth-hormone secretagogue (GHRP) / ghrelin receptor agonist | Orally active non-peptide growth-hormone secretagogue (ghrelin-receptor agonist) |
| Research category | Growth & GH-Axis | Growth & GH-Axis |
| Length (amino acids) | 5 amino acids | Not documented |
| Molecular weight | 711.9 g/mol | 624.8 g/mol (free base); approximately 936.2 g/mol as the mesylate salt |
| Half-life | ~2 hours (reported approximately 120 minutes) | Approximately 24 hours (supports once-daily dosing in studies) |
| Origin | Ipamorelin is a synthetic pentapeptide developed in the 1990s (originally by Novo Nordisk) as a selective growth-hormone secretagogue. It was designed to stimulate GH release with minimal off-target hormonal effects. | MK-677 (Ibutamoren, development code MK-0677) is an orally active, non-peptide growth-hormone secretagogue developed by Merck. It is a spiroindane/spiropiperidine small molecule, not a peptide. |
“Not documented” means the PeptiDex entry records no value for that field. Nothing on this page is estimated, and no figure is carried over from one compound to the other.
How Ipamorelin works
Ipamorelin is an agonist of the growth-hormone secretagogue receptor (GHS-R1a, the ghrelin receptor), mimicking ghrelin to stimulate GH release from the anterior pituitary. It acts on the pituitary and hypothalamus to promote a pulsatile release of growth hormone. Unlike some other GHRPs, it is reported to be highly selective, releasing GH without significantly stimulating ACTH, cortisol, or prolactin at effective doses.
How MK-677 (Ibutamoren) works
MK-677 is an agonist of the growth-hormone secretagogue receptor (GHS-R1a, the ghrelin receptor), mimicking ghrelin to stimulate pulsatile GH release from the pituitary and raise circulating IGF-1. Unlike the peptide GHRPs, it is orally bioavailable and long-acting. It can also modestly increase cortisol and appetite via ghrelin-receptor signaling.
Mechanistic descriptions reflect published research-literature understanding and are quoted from each compound's own entry. Much peptide research is preclinical (in-vitro or animal-model); mechanism in humans may differ and is not established for many compounds.
Where each one appears in the literature
The research contexts each entry documents. Listing a research area is not a claim of efficacy or a therapeutic indication, and the two lists are not scored against each other.
Ipamorelin
MK-677 (Ibutamoren)
What sets each apart
Ipamorelin
Among GHRPs, ipamorelin is noted for its selectivity — stimulating GH release without the appetite, cortisol, and prolactin elevations associated with GHRP-6 and hexarelin.
MK-677 (Ibutamoren)
Unlike the peptide secretagogues in this class, MK-677 is a non-peptide, orally active, long-acting ghrelin-receptor agonist, making its route and pharmacokinetics fundamentally different.
Frequently asked questions
What is ipamorelin and what class of compound is it?
Ipamorelin is a synthetic pentapeptide growth hormone secretagogue (a ghrelin/GHS-R1a receptor agonist). It is studied as one of the most selective GHRPs, stimulating pulsatile GH release from the anterior pituitary with minimal effect on cortisol, prolactin, or ACTH in research models.
How does ipamorelin differ from GHRP-2 and GHRP-6?
All three activate the ghrelin receptor (GHS-R1a), but ipamorelin is the most selective: in the research literature it drives GH release without the appetite stimulation seen with GHRP-6 or the cortisol/prolactin elevation associated with GHRP-2. This selectivity is why it is frequently used as a reference GHRP in study design.
Why is ipamorelin commonly studied alongside a GHRH analog like CJC-1295?
Ipamorelin (a GHS-R agonist) and a GHRH analog such as CJC-1295 or sermorelin act on two different receptor pathways. Research protocols pair them because combined GHRH + GHRP stimulation produces a synergistic, amplified GH pulse greater than either compound alone.
How does MK-677 differ from injectable GHRPs like ipamorelin?
MK-677 targets the same ghrelin receptor as injectable GHRPs but is a non-peptide small molecule with ~60-70% oral bioavailability, so it is taken by mouth rather than injected. Its long half-life sustains elevated IGF-1 across the day, unlike the discrete pulses from short-acting injectable GHRPs.
What is MK-677 (ibutamoren)?
MK-677 (ibutamoren) is an orally active, non-peptide growth hormone secretagogue that mimics ghrelin and binds the GHS-R1a receptor. Because it is a small molecule rather than a peptide, it survives digestion and is studied as an oral agent that raises GH and IGF-1 levels.
What does MK-677's long half-life imply for research?
MK-677 has a long biological half-life (reported ~24 hours of sustained IGF-1 elevation), which supports once-daily oral dosing in research protocols and produces a sustained elevation of GH/IGF-1 rather than a sharp pulse.
Answers are the ones published on each compound's own PeptiDex entry. They are educational summaries of research-literature context and are not medical advice.