MK-677 (Ibutamoren)
Also known as Ibutamoren, Ibutamoren mesylate, MK-0677, L-163,191
MK-677 (ibutamoren) is a non-peptide, orally active ghrelin-receptor secretagogue. A research profile of the one molecule in this cluster that is not a peptide at all.
MK-677, or ibutamoren, is grouped with the growth-hormone compounds because it engages the same ghrelin receptor as ipamorelin and the GHRPs — but it is fundamentally a different kind of molecule, and getting that right matters. It is not a peptide. It is a synthetic small molecule (a spiropiperidine), which changes almost everything about how it behaves.
Because that distinction is the whole story, this page is organized around it. Descriptive chemistry and research context only — no dosing, no promised effects.
MK-677 is a small-molecule spiropiperidine — a non-peptide. It is an agonist of the growth-hormone secretagogue receptor (GHS-R), the ghrelin receptor, but unlike the GHRPs and GHRH analogs in this cluster it is not built from amino acids. Its non-peptide nature is what allows it to be orally active and to carry a notably long half-life.
Same receptor, but not a peptide
MK-677 is an agonist of the growth-hormone secretagogue receptor (GHS-R) — the ghrelin receptor — which is exactly the target hit by ipamorelin, GHRP-2, GHRP-6 and hexarelin. On the receptor level, it sits squarely on the secretagogue side of this family, opposite the GHRH analogs.
The critical difference is chemical: it is not made of amino acids. It is a small-molecule spiropiperidine. Every peptide in this cluster must be handled as a lyophilized peptide and reconstituted; MK-677 is a different class of compound entirely, which is why it is described as non-peptide even though it does a peptide-like job at the receptor.
Why 'orally active' and 'long-acting' follow it around
Peptides like the GHRPs are broken down in the gut, which is why they are studied as injectables in research settings. MK-677's non-peptide structure lets it survive oral administration and gives it a long half-life — properties the peptide secretagogues do not share. Those two traits, oral activity and duration, are the practical reasons researchers treat it as distinct from the peptide GHRPs despite the shared receptor.
This is a description of the molecule's chemistry, not an endorsement of any use. But it is the cleanest way to understand why MK-677 is listed separately and studied under different conditions than ipamorelin or GHRP-2.
Identification
Because MK-677 is a defined small molecule rather than a peptide, it has no amino-acid sequence to report; it is identified by its chemical structure and mass. A certificate of analysis relies on chromatographic purity and mass confirmation of the small molecule. Verify each lot against its batch documentation.
These are research areas the compound is associated with in the literature — not medical claims or intended uses.
Handling & storage
Supplied as a small-molecule research chemical rather than a reconstituted peptide. Stored sealed and cool, away from light and moisture. Handle per accepted laboratory practice.
Verify a certificate by lot →Common questions
No. Despite being grouped with the growth-hormone peptides, MK-677 (ibutamoren) is a non-peptide small molecule — a spiropiperidine. It acts on the same ghrelin receptor but is chemically a different class.
Peptides are degraded in the gut, so the GHRPs are studied as injectables. MK-677's non-peptide structure lets it survive oral administration and gives it a long half-life.
It engages the same receptor — the ghrelin (GHS) receptor — so at the receptor level it is a secretagogue like ipamorelin. The difference is that MK-677 is a small molecule, not a peptide.
This monograph is a research-use reference. It describes composition and the contexts in which the compound has been studied — it is not medical advice, a description of effects, or a recommendation for use. Sold strictly for laboratory and research use; not for human or animal consumption.