MK-677 (Ibutamoren)
Orally active non-peptide growth-hormone secretagogue (ghrelin-receptor agonist)
An orally active ghrelin-receptor agonist studied in GH-axis research.
Also referenced as: Ibutamoren
Overview
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.
At a glance
What MK-677 (Ibutamoren) does
MK-677 (ibutamoren) is unusual in this group: it is not a peptide but a small, orally active, non-peptide molecule that mimics ghrelin at the growth hormone secretagogue receptor (GHS-R1a). By activating this receptor in the pituitary and hypothalamus it stimulates GH release and, because it is orally bioavailable with a roughly 24-hour half-life, it produces a sustained daily elevation of both GH and IGF-1 rather than a brief pulse. This durability and oral dosing are its defining pharmacologic features and the reason it has the most substantial human clinical data of any compound in this list.
In human trials MK-677 has been shown to raise GH and IGF-1 into the range of younger adults in older subjects, and — in a notable year-long study — to increase fat-free (lean) mass. However, the same trials documented that it did not improve functional strength or produce the clinical benefits hoped for, and it consistently increases appetite (via ghrelin-receptor agonism), causes fluid retention, and can raise fasting glucose and reduce insulin sensitivity. A major randomized trial in older adults with hip fracture was ultimately halted over congestive-heart-failure signals, and MK-677 failed to gain approval. So while it reliably moves the GH/IGF-1 axis in humans, its clinical outcome record is mixed-to-negative.
It has also been studied for GH deficiency, catabolic states, and sleep (it can increase slow-wave and REM sleep). It remains investigational, not an approved drug.
Effects reported in research
- Raised circulating GH and IGF-1 to youthful ranges in older adults with once-daily oral dosing (human clinical trials).
- Increased fat-free (lean) body mass over 12 months in older adults (randomized human trial).
- Did NOT improve functional muscle strength despite the lean-mass gain (human data).
- Increased appetite via GHS-R1a agonism — a consistent and pronounced effect (human).
- Caused fluid retention/edema and mild increases in fasting glucose with reduced insulin sensitivity (human).
- Increased slow-wave and REM sleep in sleep studies (human).
- A trial in frail elderly hip-fracture patients was halted over congestive-heart-failure signals; the drug was not approved.
- Orally bioavailable non-peptide with ~24 h action — sustains GH/IGF-1 rather than producing discrete pulses.
Effects listed reflect findings reported in the research literature — many in animal or in-vitro models. Listing an effect is not a claim of efficacy or a therapeutic indication in humans.
Mechanism of action
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 description reflects published research-literature understanding. Much peptide research is preclinical (in-vitro or animal-model); mechanism in humans may differ and is not established for many compounds.
What it's studied for
Research contexts in which MK-677 (Ibutamoren) appears in the literature. Listing a research area is not a claim of efficacy or a therapeutic indication.
Key characteristics
- Non-peptide small molecule that is orally active, unlike injectable GHRPs
- Long half-life (~24 h) supports once-daily use in studies
- Ghrelin-receptor (GHS-R1a) agonist that raises GH and IGF-1
- Can increase appetite and modestly raise cortisol via ghrelin signaling
- Reported side effects in trials include increased appetite, fluid retention, and insulin resistance
Reported research dosing reference only
Educational reference, not dosing guidance. The figures below summarize amounts reported in published research and research-community protocols, provided for educational and research context only. They are not medical advice, not a recommendation, and not instructions for human use. MK-677 (Ibutamoren) is a research compound.
MK-677 is referenced in the research literature as an oral agent in the ~10-25 mg once-daily range. These are reference figures for research context only, not dosing guidance for humans.
- Common research-protocol reference: 10-25 mg orally per day
- Lower-end reference in some studies: ~10 mg/day
Non-peptide small molecule, orally bioavailable (~60-70%); no reconstitution needed. Reference figures only, not human dosing guidance.
How it compares
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.
Commonly studied alongside
Compounds frequently researched together with MK-677 (Ibutamoren) in the literature. Cross-referenced for research context — not a usage or combination recommendation.
Compare and calculate
Side-by-side pages for the pairings the literature already documents for MK-677 (Ibutamoren), plus the unit-conversion reference for a reconstituted vial. Factual comparisons of documented characteristics — not a recommendation to combine or use any compound.
Handling & Stability
Storage and handling depend on the supplied form, which varies for this compound. Follow the supplier’s stated conditions and shelf life.
- Avoid repeated freeze-thaw cycles
- Verify supplier lot and Certificate of Analysis
- Follow institutional lab-safety protocols
Analytical & COA Concepts
Reputable research suppliers publish a third-party Certificate of Analysis per batch. Key analytical concepts referenced in COAs include:
Category Context
MK-677 (Ibutamoren) sits in the Growth & GH-Axis area of the PeptiDex library.
- Entry type: Research compound reference
- Growth & GH-Axis category hub →
- Browse the full library →
- Glossary of terms →
Where researchers source MK-677 (Ibutamoren)
For researchers studying MK-677 (Ibutamoren), third-party suppliers such as Practically Natty Peptides offer research-grade material, third-party tests every batch and provides Certificates of Analysis on request, and ship from the US.
PeptiDex does not maintain a direct supplier listing for this compound. The link above goes to a third-party research-supplier directory.
Frequently asked questions
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.
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 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.
Is MK-677 an approved drug?
No. MK-677 was investigated in clinical trials (for example in GH-deficiency and muscle-wasting research) but was never approved for human use. It is sold only as a research chemical.
Does MK-677 affect appetite?
Because it is a ghrelin-receptor agonist, MK-677 is reported in the research literature to increase appetite, consistent with ghrelin's role as a hunger signal. This is a commonly noted pharmacologic effect in studies.
Answers are educational summaries of research-literature context and do not constitute medical advice. See the Research Library, COA guide, and Storage & Handling guide for more.
References
Primary literature indexed in PubMed for MK-677 (Ibutamoren). Listing a study records that it exists and is indexed — it is not a claim of efficacy, a therapeutic indication, or an endorsement of its conclusions. Much of this literature is preclinical (in-vitro or animal-model).
- Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial
- The Safety and Efficacy of Growth Hormone Secretagogues
Each reference was checked against its PubMed record on 2026-07-28: the PMID resolves and the title, journal and year match. Where no indexed literature exists for a compound, PeptiDex says so rather than substituting a citation about a different molecule. See the editorial policy.