What Is MK-677 (Ibutamoren)? A Research Overview

MK-677, also called ibutamoren, is an orally-active, non-peptide growth-hormone secretagogue that mimics the hormone ghrelin at the GHS-R1a (ghrelin) receptor. It has been studied in the scientific literature as a long-acting stimulator of the growth-hormone (GH) / insulin-like growth factor-1 (IGF-1) axis. Importantly, MK-677 is a synthetic small molecule — it is not a peptide, which sets it apart from peptide secretagogues such as ipamorelin and sermorelin.

For research use only (RUO). This article is educational and summarizes published preclinical and clinical literature. Bolt Peptide does not sell MK-677. Nothing here is medical advice, a dosing protocol, or a claim of benefit for any person. Research compounds are not for human or veterinary use.

Quick facts

• Class: non-peptide ghrelin-receptor (GHS-R1a) agonist — a small molecule, not a peptide
• Route studied: orally active in published research
• Research focus: the GH / IGF-1 axis
• Other names: ibutamoren, MK-0677, L-163,191
• Status: investigational; not approved by the FDA for any use

What is MK-677?

MK-677 (ibutamoren) is a synthetic, orally-active compound developed as a growth-hormone secretagogue — a molecule that engages the same receptor as the natural hormone ghrelin. In the published literature it binds the growth-hormone-secretagogue receptor 1a (GHS-R1a) with high affinity, where it is described as a non-peptide, small-molecule agonist (Liu et al., 2021). Because it can be taken by mouth and has a long activity window, MK-677 has been characterized in studies as a way to sustain signaling along the GH/IGF-1 axis over an extended period rather than in brief pulses.

How MK-677 differs from peptide secretagogues

Many compounds discussed alongside MK-677 — including Ipamorelin and CJC-1295 — are peptides, short chains of amino acids. MK-677 is fundamentally different in two ways: it is a non-peptide small molecule (not an amino-acid chain), and it is described in the literature as orally active, whereas peptide secretagogues are typically studied via injection because they are broken down in the digestive tract. For a comparison of two peptide secretagogues researchers often reference, see CJC-1295 vs Ipamorelin.

What does the research show?

MK-677 has been examined in both clinical and preclinical investigational studies; the findings below are attributed to that published literature and are not statements about any individual. In a randomized, placebo-controlled clinical trial in healthy older adults, an oral ghrelin mimetic (MK-677) was reported to raise serum GH and IGF-1 levels and to increase fat-free mass over the study period, while the investigators noted no significant improvement in measured strength or function and reported effects on insulin sensitivity (Nass et al., 2008). In an earlier short-term clinical study, MK-677 was described as reversing diet-induced protein (nitrogen) loss in research subjects placed on calorie restriction, an effect the authors linked to elevated GH and IGF-1 (Murphy et al., 1998). These remain investigational findings reported in the scientific record — MK-677 is not an approved therapy.

Mechanisms studied in the lab

• GHS-R1a agonism: MK-677 binds and activates the ghrelin receptor (GHS-R1a), the same receptor targeted by endogenous ghrelin, as characterized structurally by Liu et al. (2021).
• Sustained GH/IGF-1 signaling: in published studies it is associated with prolonged, rather than briefly pulsatile, activation of the GH/IGF-1 axis.

Research status

MK-677 / ibutamoren is an investigational compound. It has been studied across multiple clinical and preclinical settings but is not approved by the U.S. Food and Drug Administration for any indication, and it is not a peptide. Any material referencing MK-677 in a research context would be supplied strictly as a research chemical — for in-vitro and laboratory use only, never for human or animal consumption.

Related research compounds

Bolt Peptide focuses on peptide research materials. Explore the full research peptide catalog, or read about a peptide growth-hormone-releasing analog in What is Sermorelin? for context on how peptide secretagogues are studied.

FAQ

Is MK-677 a peptide? No. MK-677 (ibutamoren) is a synthetic, non-peptide small molecule. It mimics the action of the peptide hormone ghrelin at the GHS-R1a receptor, but it is not itself a peptide.

Is MK-677 the same as ipamorelin or CJC-1295? No. Those are peptides studied as secretagogues. MK-677 acts on a related receptor pathway but is chemically distinct (a non-peptide small molecule) and is described as orally active rather than injectable.

Is MK-677 approved or sold by Bolt Peptide? MK-677 is investigational and not FDA-approved for any use. Bolt Peptide does not currently sell it; this article is provided for educational purposes only.

References

1. Nass R, 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.
2. Murphy MG, et al. MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. J Clin Endocrinol Metab. 1998.
3. Liu H, et al. Structural basis of human ghrelin receptor signaling by ghrelin and the synthetic agonist ibutamoren. Nat Commun. 2021.

For research use only — not for human or veterinary use. MK-677 (ibutamoren) is an investigational, non-peptide compound that is not FDA-approved; Bolt Peptide does not sell it. Statements have not been evaluated by the FDA.