What Is MK-677? Definition and What Research Reports

Plain definition

MK-677 is the research code name for a synthetic compound, also written MK-0677 and widely referred to as ibutamoren, that was developed to stimulate the body's own release of growth hormone when taken by mouth. Scientists call this class of molecules growth hormone secretagogues: substances that prompt the pituitary gland to secrete growth hormone rather than supplying growth hormone itself. The compound has been examined in laboratory animals and in human clinical trials, and it appears in the doping-control and toxicology literature because it also circulates in unapproved consumer products. It is a defined chemical entity with a research history, not an approved medicine.

This page is for educational purposes only and is not medical advice; consult a licensed physician about any health decision. Nothing here describes how the compound should be obtained, prepared or administered.

What MK-677 is in biochemical terms

In the published literature, MK-677 is characterised as an orally active growth hormone secretagogue — a description used directly in the titles of both a rat somatic-growth study (PMID 30450851) and an equine hair-detection study (PMID 36354265). Two features define it structurally and functionally:

• It is a small synthetic molecule, not a peptide. Growth hormone secretagogues such as GHRP-2, GHRP-6 and hexarelin are short chains of amino acids; MK-677 is a non-peptide compound designed to survive digestion, which is why the literature describes it as orally active.
• It acts upstream of growth hormone. Secretagogues are studied as stimulators of endogenous hormone release rather than as hormone replacements, which is the conceptual reason researchers have tested the compound in settings involving growth and body composition (PMID 30450851, PMID 36303408).

Names and spellings

Regulatory and research status

MK-677 is not an approved prescription medicine; it has been studied in clinical trials but has not reached market authorisation as a therapeutic product. Material labelled with the name is generally described as "for research use only," a designation that means it has not been evaluated for human administration. The compound also appears in analytical chemistry because testing laboratories have needed methods to identify it: one study developed and applied an approach for detecting MK-0677 in equine hair after oral administration, illustrating that the compound is a target analyte in drug-testing contexts (PMID 36354265). Specific prohibited-list classifications, national scheduling and sport-federation rules vary by jurisdiction and by organisation and are not detailed here.

How the term is used in peptide research

Within research writing, "MK-677" is used in three recognisable ways:

1. As a pharmacological tool. Because the compound stimulates endogenous growth hormone release and can be given by mouth, it has been used in animal work to probe growth-axis physiology. A rat study examined the effect of the orally active secretagogue on somatic growth (PMID 30450851).
2. As a candidate therapeutic. It has been tested in randomized controlled trials for conditions in which growth hormone signalling was hypothesised to matter. A randomized trial in Alzheimer's disease reported no clinical effect on disease progression (PMID 19015485).
3. As an analyte or exposure variable. Toxicology case reports and doping-control papers refer to MK-677 as a substance detected or implicated, rather than as an intervention the researchers administered (PMID 40675653, PMID 36354265).

Where the term is misused

• Calling it a peptide. MK-677 is routinely listed alongside peptides in online glossaries, but it is a non-peptide small molecule. The grouping reflects shared interest in the growth hormone axis, not shared chemistry.
• Calling it a SARM. Selective androgen receptor modulators such as LGD-4033 act on the androgen receptor; MK-677 is a secretagogue. The confusion is reinforced because the two classes are often reported together, as in a case report describing combined LGD-4033 and MK-677 exposure (PMID 36303408).
• Describing it as growth hormone. It is not recombinant growth hormone and is not a hormone product; the literature frames it as a stimulator of endogenous secretion.
• Treating trial participation as evidence of approval. Being studied in a randomized trial is not the same as being approved, and the Alzheimer's trial specifically reported no clinical effect on progression (PMID 19015485).

What the published literature reports

The verified publications summarised on this page span animal work, a randomized human trial, analytical detection and clinical case reporting. The table below states only what each paper's title and abstract scope described; no numerical doses are reproduced because they are outside the scope summarised here.

What this body of evidence does and does not establish

Case reports describe single individuals and cannot establish how commonly an outcome occurs; they are hypothesis-generating (PMID 36303408, PMID 40675653). Animal studies describe physiology in a different species and do not translate directly to people (PMID 30450851). The one randomized human trial listed here addressed a specific neurological question and reported a negative clinical result (PMID 19015485), which does not speak to other proposed applications.

Adverse events associated with MK-677: What Studies Report

The most direct safety report among the verified publications is a 2025 BMJ Case Reports description of hepatotoxicity — liver injury — attributed to MK-677 in a single patient (PMID 40675653). A separate case report in Experimental Physiology documented changes in body composition and in circulating biomarkers in an individual who had used LGD-4033 together with MK-677, meaning the biomarker changes described there cannot be attributed to one compound alone (PMID 36303408). Neither report quantifies risk across a population. In the randomized Alzheimer's disease trial, researchers reported no clinical effect on progression as the primary finding (PMID 19015485).

Related terms

• Growth hormone secretagogue (GHS) — the pharmacological class MK-677 belongs to, described as such in study titles (PMID 30450851).
• Ibutamoren — the common non-code name for the same compound.
• LGD-4033 — a selective androgen receptor modulator reported alongside MK-677 in a case report (PMID 36303408).
• Drug-testing analyte — the role MK-0677 plays in analytical studies such as hair detection work in horses (PMID 36354265).
• Research use only (RUO) — a labelling designation indicating material has not been evaluated for human administration.

References

• Hepatotoxicity induced by MK-677 (BMJ Case Reports, 2025)
• LGD-4033 and MK-677 use impacts body composition, circulating biomarkers, and skeletal muscle androgenic hormone and receptor content: A case report (Experimental Physiology, 2022)
• Effect of the Orally Active Growth Hormone Secretagogue MK-677 on Somatic Growth in Rats (Yonsei Medical Journal, 2018)
• Detection of the growth hormone secretagogue MK-0677 in equine hair following oral administration (Drug Testing and Analysis, 2023)
• Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial (Neurology, 2008)