MK-677

MK-677 (Ibutamoren / Nutrobal) — Research Overview

Abstract

MK-677 (Ibutamoren, commonly marketed as Nutrobal) is an orally active, non-peptide ghrelin receptor (GHS-R1a) agonist and growth-hormone secretagogue. It stimulates pulsatile growth hormone (GH) release and increases circulating insulin-like growth factor-1 (IGF-1) in humans and animals. Because of its oral bioavailability and prolonged GH-releasing effects without activation of the hypothalamic–pituitary–adrenal axis, MK-677 is widely used as a research tool to study GH/IGF-1 physiology, aging-related sarcopenia, metabolism, and recovery biology. This review summarizes chemistry, mechanism, preclinical and clinical findings, potential research applications and safety considerations. For research use only.

Chemical identity

Common names: MK-677, Ibutamoren, Nutrobal
Development code: MK-677 (Merck)
IUPAC / chemical class: Non-peptide, orally active small-molecule ghrelin receptor agonist
CAS Number: 159752-10-0
Molecular formula (typical listing): C₂₇H₃₆N₄O₅S (varies with salt/formulation)
Synonyms / trade names: Ibutamoren mesylate (often encountered as the free base or salt)

Mechanism of action

MK-677 is a selective agonist of the ghrelin receptor (GHS-R1a). Activation of this receptor in the pituitary and hypothalamus promotes release of growth hormone–releasing hormone (GHRH) signaling and stimulates endogenous pulsatile GH secretion. Downstream effects include increased circulating IGF-1 (hepatic response) with modest changes in cortisol. Important mechanistic notes for researchers:

GHS-R1a activation → increased GH pulsatility (amplitude and/or frequency depending on species/age).
Increases IGF-1 via hepatic induction following GH rise.
Does not mimic ghrelin fully (some central and appetite effects are seen but differ by dose/species).
Oral bioavailability and long effective half-life (~24 hours reported in human studies) make it a convenient research agent for chronic administration studies (preclinical or controlled clinical trials).

Pharmacokinetics (summary from human/animal studies)

Route: orally active
Absorption: effective oral absorption; peak concentrations several hours post-dose in humans.
Half-life / persistence: relatively long effective half-life enabling once-daily dosing in studies (human PK data report prolonged GH/IGF-1 effects).
Distribution & metabolism: hepatic metabolism; metabolites vary by species.
Elimination: renal & hepatic routes dependent on species and formulation.

Key preclinical & clinical findings (selected, high-level)

GH & IGF-1 induction: Repeated oral MK-677 increases overnight GH and daytime IGF-1 in humans and animals.
Body composition: In older adults and certain patient groups, MK-677 increased fat-free mass (lean mass) in several studies, with variable effects on fat mass.
Bone metabolism: Some studies show increases in markers of bone formation and possible improvements in bone mineral density with prolonged exposure in preclinical models; clinical translation remains under investigation.
Sleep: Modest changes in sleep architecture (e.g., increases in REM or slow-wave sleep reported in some studies), potentially related to GH physiology.
Metabolic safety: GH/IGF-1 elevation can influence glucose metabolism; some studies report mild reductions in insulin sensitivity or transient increases in fasting glucose — important endpoints for safety monitoring.
Clinical trial history: MK-677 has been used in multiple clinical research contexts (older adults, GH deficiency models) but is not an approved therapeutic for general use.

Potential research applications

Aging & sarcopenia models — investigate mechanisms of age-related lean mass loss and interventions that restore anabolic signaling.
Musculoskeletal repair — study GH/IGF-1-mediated tissue repair, tendon/ligament recovery models, and bone turnover.
Metabolic regulation — examine GH axis modulation on substrate utilization, adipose biology, and energy expenditure.
Sleep physiology — explore GH-linked changes in sleep architecture and downstream restorative effects.
Endocrine interaction studies — map downstream transcriptional and proteomic changes following chronic GH/IGF-1 increases.

Benefits (research context only)

Sustained elevation of endogenous GH/IGF-1 without peptide injections.
Orally active, enabling longer term studies without parenteral administration.
Proven translational signal (demonstrated lean mass gains in human trials) making it a useful tool compound for anabolic/repair research.
Versatile model to study GH axis effects across tissues (muscle, bone, brain, adipose).

Risks / safety considerations

Not approved for human therapeutic use outside controlled clinical trials. All research must be done under institutional review.
Metabolic effects: GH/IGF-1 elevation may impair glucose tolerance or reduce insulin sensitivity in some subjects; monitor fasting glucose, HbA1c, and insulin markers.
Edema / fluid retention: observed in some anabolic GH-stimulating contexts — monitor weight and electrolyte balance.
Carcinogenicity & proliferative risk: chronic GH/IGF-1 stimulation is biologically plausable to affect proliferative pathways — long-term oncologic risk is not established and merits caution.
Drug interactions / off-target effects: full interaction profile is incomplete; evaluate coadministered agents carefully.
Ethical & regulatory: MK-677 is on lists of prohibited enhancement agents for sport; research use must be documented and comply with local law.

Recommended research endpoints & monitoring (for study design)

Primary: serum GH (pulsatility metrics), IGF-1 levels, body composition (DXA), muscle strength/function tests.
Safety: fasting glucose, insulin, HOMA-IR, liver enzymes, renal panel, electrolytes, cardiac monitoring if indicated.
Secondary: bone turnover markers, sleep polysomnography (if sleep is of interest), transcriptomics/proteomics in muscle or liver biopsies.
Duration considerations: short-term endocrine effects are clear; long-term safety and proliferative endpoints require extended follow-up and histopathology in animal studies.

Regulatory & procurement notes

MK-677 is a research chemical and is sold by suppliers labelled “for research use only — not for human consumption”.
Investigators should obtain institutional approvals, ethical review board clearance, and follow all relevant regulations before obtaining or using MK-677 in any study.

SEO keywords & meta description

Primary keywords: MK-677 research, Ibutamoren, Nutrobal, ghrelin receptor agonist, MK-677 CAS 159752-10-0.
Secondary / long-tail: MK-677 effects on lean mass, MK-677 GH IGF-1 studies, MK-677 aging research, Ibutamoren research compound.
Meta description (suggested):

MK-677 (Ibutamoren, CAS 159752-10-0) is an oral ghrelin receptor agonist studied for GH/IGF-1 induction, body composition effects, and aging-related research. For research use only.

10 Frequently Asked Questions (FAQ)

1. What is MK-677 (Ibutamoren)?
MK-677 is an orally active ghrelin receptor (GHS-R1a) agonist that stimulates endogenous growth hormone (GH) release and increases circulating IGF-1. It is used as a research tool to study GH axis physiology.

2. What is the CAS number for MK-677?
159752-10-0

3. How does MK-677 differ from injectable GH or GH-releasing peptides?
Unlike parenteral GH or GH-releasing peptides, MK-677 is a small-molecule oral agonist of the ghrelin receptor that promotes endogenous, pulsatile GH release, avoiding daily injections of peptide GH in research settings.

4. What research benefits has MK-677 demonstrated?
In controlled research, MK-677 increases GH and IGF-1 and has been associated with increases in fat-free (lean) mass in some human studies, making it useful in sarcopenia and metabolic research models.

5. Is MK-677 approved for medical or human enhancement use?
No. MK-677 is not an FDA-approved therapy for general clinical use and is classified as a research chemical.

6. What are the main safety concerns to monitor in studies?
Monitor glucose/insulin metabolism (risk of reduced insulin sensitivity), fluid retention, liver and renal function, and any unexpected proliferative or oncologic signals in long-term studies.

7. Does MK-677 affect appetite or weight?
MK-677 can increase appetite in some individuals and may affect body weight through combined effects on lean mass and appetite; appetite outcomes can vary between species and study protocols.

8. Can MK-677 improve bone health?
Preclinical and some clinical evidence suggests GH/IGF-1 activation can influence bone formation markers; however, robust long-term human data on bone mineral density with MK-677 are limited.

9. What endpoints should a rigorous MK-677 study include?
Key endpoints include GH pulsatility profiling, IGF-1 measurement, body composition (DXA), metabolic panels (glucose/insulin), and safety labs; for long-term studies add histopathology and cancer surveillance endpoints in animals.

10. How should researchers obtain and store MK-677?
Source from reputable research chemical suppliers with Certificates of Analysis. Store per vendor instructions (commonly desiccated, refrigerated or frozen for extended storage) and maintain chain-of-custody and regulatory documentation.

References & further reading (select, representative)

(Representative topics and landmark study types — researchers should consult primary literature and databases for full citations.)

Human clinical trials and phase-1/2 research demonstrating GH and IGF-1 elevation and body composition effects.
Preclinical mechanistic papers on ghrelin receptor pharmacology and small-molecule GHS-R1a agonists.
Reviews on GH axis modulation for aging and sarcopenia.

Disclaimer

This document is intended for educational and laboratory research purposes only. It is not medical advice, endorsement, or a dosing guide. MK-677 is not approved for human or veterinary use outside of regulated clinical trials. Always conduct research under appropriate institutional approvals and safety protocols.