The short answer
MK-677, also called ibutamoren or MK-0677, is a growth-hormone secretagogue — it prompts the body to release its own growth hormone. But chemically it is a small molecule (a spiropiperidine), not a peptide.[1][3] That single fact matters: it's why MK-677 works as a pill, when nearly all peptide growth-hormone secretagogues have to be injected.
Why is MK-677 confused with peptides?
The confusion is understandable. MK-677 is sold on the same "research chemical" websites as peptides, it's stacked with them in bodybuilding, and — crucially — it acts on the same target as several peptides: the ghrelin / growth-hormone-secretagogue receptor.[2] In other words, it does a similar job to peptides like ipamorelin and GHRP-6 — but through a completely different kind of molecule.
MK-677 vs peptide GH secretagogues
Here's the key contrast:
| MK-677 (ibutamoren) | Peptide GH secretagogues | |
|---|---|---|
| Chemical type | Small molecule (spiropiperidine) | Peptides (amino-acid chains) |
| Examples | MK-677 / ibutamoren | Ipamorelin, GHRP-6, hexarelin |
| How it's taken | Oral (a pill) | Injected (broken down if swallowed) |
| Target | Both act on the ghrelin / GH-secretagogue receptor | |
So MK-677 belongs in the same functional conversation as growth-hormone peptides, but it is not one of them. Explore the actual peptides in the muscle-growth category, and see the related non-peptides below.
What about SARMs, and is it legal?
MK-677 is also frequently — and wrongly — called a SARM (selective androgen receptor modulator). It isn't that either; SARMs act on the androgen receptor, while MK-677 acts on the ghrelin receptor. It's simply a growth-hormone secretagogue.
Like the peptides it's grouped with, MK-677 is not FDA-approved, is sold as a research chemical, and is banned in sport by WADA. It's a useful reminder that "sold on a peptide site" does not make something a peptide. See peptides vs SARMs and what are peptides?
Frequently asked questions
Is MK-677 a peptide?
No. MK-677 (ibutamoren) is an orally active small molecule — a spiropiperidine — not a peptide. It's a growth-hormone secretagogue that acts on the same receptor as some peptides, which is why it's often confused with them, but chemically it is not a peptide.
Is ibutamoren the same as MK-677?
Yes. Ibutamoren, MK-677, and MK-0677 are names for the same compound: an orally active growth-hormone secretagogue that is a small molecule, not a peptide.
What is the difference between MK-677 and ipamorelin?
Both prompt growth-hormone release by acting on the ghrelin receptor, but MK-677 is a small molecule taken as a pill, while ipamorelin is a peptide that must be injected. They do a similar job through very different kinds of molecule.
Is MK-677 a SARM?
No. MK-677 is often wrongly called a SARM, but SARMs act on the androgen receptor while MK-677 acts on the ghrelin / growth-hormone-secretagogue receptor. It is a growth-hormone secretagogue, not a SARM and not a peptide.
Is MK-677 legal?
MK-677 is not FDA-approved and is sold as a 'research chemical,' the same legal grey area as many peptides, and it is banned in sport by WADA. Its legal status varies by country.
Further reading
Selected peer-reviewed sources on this topic, labelled by type. A citation is a reference, not an endorsement.
- Murphy MG, Plunkett LM, Gertz BJ, et al. MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. J Clin Endocrinol Metab. 1998. Peer-reviewed study
- Nass R, Pezzoli SS, Oliveri MC, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med. 2008. Peer-reviewed study
- Smith RG. Development of growth hormone secretagogues. Endocr Rev. 2005. Peer-reviewed study