C27H36N4O5S · 528.7 g/mol · PubChem CID 178024 ↗
MK-677
also known as Ibutamoren, MK-0677, Ibutamoren Mesylate, L-163191
Orally active, non-peptide ghrelin-receptor (GHSR-1a) agonist that stimulates pulsatile growth-hormone secretion and raises IGF-1, developed by Merck as MK-0677. Not a peptide — a small molecule; unlike injectable GH secretagogues it is taken by mouth once daily. MK-677 never reached a marketed indication despite a large clinical program. A two-year randomized trial in healthy older adults (Nass 2008) restored IGF-1 to young-adult levels and increased fat-free mass. [nass-2008-mk677]
- Class
- Ghrelin Receptor Agonist
- Evidence level
- Phase 2 clinical
- Regulatory status
- Not FDA-approved (US) — research use only
At a glance
Oral · Once daily
Primary target — Ghrelin receptor (GHSR-1a) [liu-2021-ghsr].
Pathway — Ghrelin-mimetic agonism of GHSR-1a on pituitary somatotrophs → pulsatile GH release → hepatic IGF-1 production [liu-2021-ghsr][svensson-2003-mk677].
Downstream effect — Sustained IGF-1 elevation, increased fat-free mass, increased appetite; GH secretory pattern stays pulsatile [nass-2008-mk677][murphy-1998-mk677].
Origin — Small-molecule ghrelin-receptor agonist developed by Merck (MK-0677); orally bioavailable, non-peptide [philip-2022-ibutamoren].
Feedback intact — GH-axis feedback preserved — secretion remains pulsatile and subject to somatostatin, unlike exogenous GH [svensson-2003-mk677].
| Parameter | Value |
|---|---|
| Standard dose | 25 mg / day oral [nass-2008-mk677]Dose used in the 1-year older-adult RCT. |
| Frequency | Once daily |
| Timing | Often taken before sleep (GH pulse + appetite) — timing is preference, not efficacy-critical |
| Lower / starter dose | 10–12.5 mg / day |
| Evidence basis | Human RCTs through phase IIb (e.g. hip-fracture recovery) [adunsky-2011-mk677] |
| Duration | Studied continuously up to 12 months (Nass 2008) |
| Form | Oral capsule / solution |
| Half-life | ~4–6 h (single daily dose sustains 24-h IGF-1 elevation) |
Reconstitution
A pure mass-to-volume utility. Enter what you have in the vial; the atlas computes the volume per dose. No prescription information.
- — Active malignancy (GH / IGF-1 axis stimulation)
- — Pregnancy / breastfeeding
- — Diabetes / impaired glucose tolerance (worsens insulin sensitivity)
- — Congestive heart failure or edema-prone states (fluid retention)
- — Untreated hepatic impairment
- 01Form
Oral — capsule or solution. No reconstitution or injection.
- 02Administration
Swallow once daily with water; food not required.
- 03Timing
Commonly dosed before sleep; timing is a preference, not efficacy-critical.
- 04Storage
Room temperature ≤25 °C, dry, out of light.
- 05Monitoring
Track fasting glucose / HbA1c and signs of fluid retention with chronic use.
Frequently asked
How does MK-677 work?
MK-677 acts on Ghrelin receptor (GHSR-1a), signalling via Ghrelin-mimetic agonism of GHSR-1a on pituitary somatotrophs → pulsatile GH release → hepatic IGF-1 production. [liu-2021-ghsr][liu-2021-ghsr][svensson-2003-mk677]
Is MK-677 FDA-approved?
MK-677 is not FDA-approved in the United States and is handled as a research compound (research use only). Regulatory status may differ in other jurisdictions.
Sources
of 40 rendered claims carry a resolvable citation.
- [adunsky-2011-mk677]Adunsky 2011 — MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study
Arch Gerontol Geriatr, 2011
Multicenter phase IIb RCT in hip-fracture recovery. Illustrates the scale of MK-677's human trial program; the functional-recovery endpoints did not translate into a marketed indication. - [cobani-2025-mk677]Cobani 2025 — Hepatotoxicity induced by MK-677
BMJ Case Rep, 2025
Case report of drug-induced liver injury attributed to unregulated MK-677 use — a documented real-world harm signal from consumer-market product. - [liu-2021-ghsr]Liu 2021 — Structural basis of human ghrelin receptor signaling by ghrelin and the synthetic agonist ibutamoren
Nat Commun, 2021
Cryo-EM structures of the human ghrelin receptor (GHSR-1a) bound to ghrelin and to ibutamoren (MK-677), defining the molecular basis of MK-677's receptor agonism. - [murphy-1998-mk677]Murphy 1998 — MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism
J Clin Endocrinol Metab, 1998
Oral MK-677 attenuated the nitrogen wasting of dietary caloric restriction, demonstrating an anabolic/ nitrogen-retention effect of sustained GH/IGF-1 elevation. - [nass-2008-mk677]Nass 2008 — Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults
Ann Intern Med, 2008
MK-677 2-yr trial in elderly: lean mass + IGF-1 elevation, glucose intolerance. - [philip-2022-ibutamoren]Philip 2022 — Characterization of growth hormone secretagogue small molecule ibutamoren (MK-0677) and its possible metabolites in thoroughbred horses for doping control
Rapid Commun Mass Spectrom, 2022
Analytical characterization of ibutamoren (MK-0677) and its metabolites — confirms the small-molecule identity and the compound's status as a monitored doping agent. - [sevigny-2008-mk677]Sevigny 2008 — Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial
Neurology, 2008
12-month RCT in Alzheimer's disease. MK-677 reliably raised IGF-1 but produced no cognitive benefit — a clean negative efficacy result and evidence that sustained IGF-1 elevation is not universally beneficial. - [sigalos-2018]Sigalos 2018 — The safety and efficacy of growth hormone secretagogues
Sex Med Rev, 2018
Review of GH secretagogue safety/efficacy (ipamorelin, CJC-1295, GHRP-2/6, MK-677). Class profile: increased appetite, transient edema, elevated blood glucose / reduced insulin sensitivity, modest cortisol elevation. - [svensson-2003-mk677]Svensson 2003 — The effect of treatment with the oral growth hormone (GH) secretagogue MK-677 on GH isoforms
Growth Horm IGF Res, 2003
MK-677 stimulated endogenous GH secretion across GH isoforms, consistent with a ghrelin-receptor-mediated, pulsatile pattern rather than exogenous GH administration.