MK-677

Overview

MK-677 (ibutamoren, MK-0677, L-163,191) is an orally active, non-peptide small-molecule growth hormone secretagogue developed by Merck in the 1990s. It is a spiropiperidine ghrelin-receptor (GHSR-1a) agonist — not a peptide and not a SARM, though it is commonly misclassified as both in grey-market retail. Merck discontinued development after mixed efficacy and adverse metabolic / cardiovascular findings; it is not FDA-approved.

Mechanism of Action

MK-677 is a selective agonist of the ghrelin receptor (GHSR-1a) on pituitary somatotrophs and hypothalamic neurons, driving pulsatile GH release and secondary IGF-1 elevation with once-daily oral dosing. Oral bioavailability is sufficient for sustained 24-hour effect. Unlike GHRPs, it does not significantly raise cortisol or prolactin at typical doses. It also stimulates appetite through hypothalamic ghrelin signaling.

Research Summary

MK-677 has meaningful human data from Merck-sponsored Phase I/II trials. Murphy et al. (JCEM 1998, PMID 9467534) showed 25 mg MK-677 reversed nitrogen wasting during caloric restriction in healthy adults. Svensson et al. (JCEM 1998, PMID 9467542) reported ~40% IGF-1 elevation, increased fat-free mass, and higher energy expenditure over 8 weeks in obese men. Copinschi et al. (Neuroendocrinology 1997, PMID 9349662) documented improved slow-wave and REM sleep in young and older adults. Nass et al. (Ann Intern Med 2008, PMID 18981485) — the pivotal 2-year randomized trial in 65 healthy older adults — restored GH and IGF-1 to young-adult levels and increased fat-free mass, but produced modest fasting glucose elevation and insulin resistance. The Adunsky et al. Phase IIb hip-fracture trial (Arch Gerontol Geriatr 2011, PMID 21067829) was stopped early after a congestive-heart-failure safety signal (4/62 ibutamoren vs 1/60 placebo). Merck discontinued development. MK-677 is commonly mislabeled as a 'SARM' in grey-market retail — it is not; it is a ghrelin-receptor agonist and oral GH secretagogue. It has never been FDA-approved.

Prescribers who offer MK-677

26 prescribers in our directory work with MK-677, each confirmed from their own website. Peptides like MK-677 require a prescription from a licensed provider — telehealth options are available.

Reported Side Effects

• Marked appetite increase (ghrelin-mediated)
• Water retention, edema, and fluid-driven weight gain
• Elevated fasting glucose and reduced insulin sensitivity
• Lethargy and drowsiness
• Paresthesias (numbness/tingling in extremities)
• Muscle aches and joint stiffness (fluid-related)
• Worsening of pre-existing congestive heart failure (documented trial signal)

Compare MK-677 with Others

Research References

• Murphy et al. — MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism (JCEM 1998) (1998)
• Nass et al. — Effects of an oral ghrelin mimetic (MK-677) on body composition and clinical outcomes in healthy older adults (Ann Intern Med 2008) (2008)
• Svensson et al. — Two-month treatment of obese subjects with the oral GH secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure (JCEM 1998) (1998)
• Copinschi et al. — Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man (Neuroendocrinology 1997) (1997)
• Adunsky et al. — MK-0677 (ibutamoren mesylate) for patients recovering from hip fracture: Phase IIb trial halted early for CHF safety signal (Arch Gerontol Geriatr 2011) (2011)

Frequently asked questions

Has MK-677 been independently lab-tested?

Disclosed Labs has collected 5 Certificates of Analysis (COA) for MK-677 from 3 independent testing labs. 3 vendors have submitted material for testing. Products average 98.3% tested purity across the corpus. Full testing data is available at https://www.disclosedlabs.com/peptides/mk-677/testing.

What is the average purity of MK-677 on the market?

Based on 5 COAs analyzed by Disclosed Labs, MK-677 products average 98.3% (±0.3%) tested purity. Individual vendor results vary; see per-vendor COA data at https://www.disclosedlabs.com/peptides/mk-677/coas.

Which prescribers offer MK-677 with a prescription?

26 prescribers in the Disclosed Labs directory work with MK-677, each confirmed from their own website, with telehealth options available. MK-677 requires a prescription from a licensed provider. Browse them at https://www.disclosedlabs.com/prescribers?peptide=MK-677.

How does MK-677 work?

MK-677 is a selective agonist of the ghrelin receptor (GHSR-1a) on pituitary somatotrophs and hypothalamic neurons, driving pulsatile GH release and secondary IGF-1 elevation with once-daily oral dosing. Oral bioavailability is sufficient for sustained 24-hour effect. Unlike GHRPs, it does not significantly raise cortisol or prolactin at typical doses. It also stimulates appetite through hypothalamic ghrelin signaling.

What does the research say about MK-677?

MK-677 has meaningful human data from Merck-sponsored Phase I/II trials. Murphy et al. (JCEM 1998, PMID 9467534) showed 25 mg MK-677 reversed nitrogen wasting during caloric restriction in healthy adults. Svensson et al. (JCEM 1998, PMID 9467542) reported ~40% IGF-1 elevation, increased fat-free mass, and higher energy expenditure over 8 weeks in obese men. Copinschi et al. (Neuroendocrinology 1997, PMID 9349662) documented improved slow-wave and REM sleep in young and older adults. Nass et al. (Ann Intern Med 2008, PMID 18981485) — the pivotal 2-year randomized trial in 65 healthy older adults — restored GH and IGF-1 to young-adult levels and increased fat-free mass, but produced modest fasting glucose elevation and insulin resistance. The Adunsky et al. Phase IIb hip-fracture trial (Arch Gerontol Geriatr 2011, PMID 21067829) was stopped early after a congestive-heart-failure safety signal (4/62 ibutamoren vs 1/60 placebo). Merck discontinued development. MK-677 is commonly mislabeled as a 'SARM' in grey-market retail — it is not; it is a ghrelin-receptor agonist and oral GH secretagogue. It has never been FDA-approved.