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hormone

MK-677

Also known as: Ibutamoren, Ibutamoren mesylate, MK-0677, L-163191
Moderate evidence FDA: Not FDA-approved; research-only WADA: Prohibited at all times
Last updated · 2026-06-19

MK-677 (Ibutamoren; development code MK-0677/L-163191) is an orally-active, non-peptide ghrelin-receptor agonist and growth hormone (GH) secretagogue developed by Merck in the 1990s. It binds the growth hormone secretagogue receptor (GHS-R1a) and amplifies the pituitary's own pulsatile GH release, raising circulating IGF-1. Its distinguishing feature among GH secretagogues is oral bioavailability and a long half-life — it works as a once-daily pill, unlike injectable GH-releasing peptides such as Ipamorelin or GHRP-2. Unlike most research-chemical peptides, MK-677 has a genuine body of human clinical-trial evidence, including a 2-year randomized controlled trial in older adults and a 563-patient Alzheimer's trial. That evidence tells

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Molecular weight 528.66 Da
Half-life ~4-6 hours single
CAS number 159752-10-0
Route Oral
Where to buy MK-677 →Limitless Life Nootropics · save 15% code vialbase15
02

Dosing

FREQUENCY 1x daily
CYCLE LENGTH Commonly cited as 8-12 week blocks with breaks; long-term continuous use carries metabolic risk

25 mg once daily orally is the dose used in nearly every published human trial. 10 mg/day is a common lower research dose. Oral, no reconstitution required (sold as capsules/solution in the research-chemical market). These are commonly cited research protocols, NOT trial-validated therapeutic doses or medical advice — MK-677 is not FDA-approved for any use.

03

Mechanism

Orally-active, non-peptide ghrelin-receptor (GHS-R1a) agonist / growth hormone secretagogue. Mimics ghrelin at the pituitary and hypothalamus to amplify pulsatile growth hormone (GH) release, which raises insulin-like growth factor-1 (IGF-1). Unlike injectable GHRPs (ipamorelin, GHRP-2/6) it is orally bioavailable and long-acting. Sustained IGF-1 elevation of ~40-90% is the consistent, well-replicated human finding across multiple RCTs.

04

Research summary

Study Type Year Key Finding
MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Randomized, double-blind, placebo-controlled multicenter phase IIb clinical trial 2011 The trial was terminated early due to a safety signal of congestive heart failure in a limited number of patients, and the authors conclude MK-0677 has an unfavorable safety profile in this patient population
The Safety and Efficacy of Growth Hormone Secretagogues. Narrative review of clinical studies on growth hormone secretagogues in human subjects 2018 Few long-term, rigorously controlled studies have examined the efficacy and safety of growth hormone secretagogues, including the orally available small-molecule drug ibutamoren mesylate
Hepatotoxicity induced by MK-677. Case report (single patient, drug-induced liver injury) 2025 An otherwise healthy man in his early 30s developed transaminitis after consuming MK-677 for 2 months before presentation
MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. Double-blind, randomized, placebo-controlled two-period crossover trial in 8 healthy volunteers (very small sample) 1998 Only 8 healthy volunteers (ages 24-39 yr) were studied, in a two-period crossover with 14 days of caloric restriction (18 kcal/kg.day) per period and MK-677 25 mg once daily or placebo during the last 7 days of each period
05

Sourcing

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What bloodwork do I need?

Reference ranges are general guidelines. Consult your physician for interpretation.

PRE-CYCLE
  • IGF-1
  • Fasting Glucose
  • Fasting Insulin
  • HbA1c
  • CMP
  • CBC
  • Lipid Panel
  • Prolactin
DURING CYCLE
  • IGF-1
  • Fasting Glucose
  • Fasting Insulin
  • HbA1c
  • Prolactin
POST-CYCLE
  • IGF-1
  • Fasting Glucose
  • HbA1c
  • Lipid Panel
Safety & Regulatory Status
FDA STATUS Not FDA-approved; research-only. Ibutamoren mesylate is on FDA's interim Category 2 list — substances FDA has identified as raising significant safety risks and intends to act against in compounding. No lawful compounding route.
WADA STATUS Prohibited at all times (WADA S2 — growth hormone secretagogues/mimetics, S2.2)

Regulatory status for MK-677 may change. Verify current status with your jurisdiction before use. This is not legal or medical advice.

Frequently Asked Questions

What is MK-677?
MK-677 (Ibutamoren) is an orally-active, non-peptide growth hormone secretagogue. It activates the ghrelin receptor (GHS-R1a) to amplify the body's own pulsatile growth hormone release, which in turn raises IGF-1. Its defining feature is that it works orally and is long-acting, unlike injectable GH-releasing peptides. It is not FDA-approved.
How does MK-677 work?
MK-677 is a ghrelin mimetic. It binds the GHS-R1a receptor in the pituitary and hypothalamus and stimulates the pituitary to release growth hormone in a physiologic, pulsatile pattern. The downstream rise in IGF-1 (insulin-like growth factor-1) drives most of its biological effects. In human trials, 25 mg/day raised IGF-1 by roughly 40-90% and increased fat-free mass.
What does the research on MK-677 show?
MK-677 has real human RCT data. A 2-year trial in healthy older adults (Nass 2008, Annals of Internal Medicine) showed it restored GH/IGF-1 to young-adult levels and increased fat-free mass by about 1 kg, but did not improve strength or function. A 563-patient Alzheimer's trial (Sevigny 2008) raised IGF-1 ~73% but produced no cognitive benefit. It reliably raises bone-turnover markers and IGF-1, but a hip-fracture trial (Adunsky 2011) was halted early for a congestive-heart-failure safety signal. Bottom line: the biomarker effect is real, the functional/clinical benefit is largely unproven, and there are genuine metabolic and cardiac concerns.
How is MK-677 dosed?
Nearly every published human trial used 25 mg once daily, taken orally; 10 mg/day is a common lower research dose. No injection or reconstitution is needed. These figures reflect commonly cited research protocols, not trial-validated therapeutic doses or medical advice — consult a clinician.
What are the side effects of MK-677?
Documented effects include increased appetite (it is a ghrelin mimetic), fluid retention and edema, transient muscle/joint aches, lethargy, and mildly elevated prolactin after initial doses. The most important concerns are metabolic — increased fasting glucose and reduced insulin sensitivity (it can push toward insulin resistance, especially with long-term use) — and a congestive-heart-failure safety signal that ended one hip-fracture trial early. Monitor IGF-1, fasting glucose, insulin, and HbA1c.
Is MK-677 FDA-approved?
No. MK-677 is not FDA-approved for any indication; development for sarcopenia and frailty was discontinued. It is sold only as a research chemical. Ibutamoren mesylate is also on FDA's interim Category 2 list — the list of nominated bulk substances FDA has identified as raising significant safety risks and intends to take action against — so there is no lawful compounding route for MK-677. It is technically not a peptide (it is a non-peptide peptidomimetic) but is commonly grouped with peptides. It is prohibited in sport at all times by WADA (category S2, growth hormone secretagogues).

References

  1. Adunsky A, Chandler J, Heyden N, et al.. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study.. Archives of gerontology and geriatrics (2011). PMID: 21067829
  2. Sigalos JT, Pastuszak AW. The Safety and Efficacy of Growth Hormone Secretagogues.. Sexual medicine reviews (2018). PMID: 28400207
  3. Cobani E, Amin MS, Hasso M, et al.. Hepatotoxicity induced by MK-677.. BMJ case reports (2025). PMID: 40675653
  4. Murphy MG, Plunkett LM, Gertz BJ, et al.. MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism.. The Journal of clinical endocrinology and metabolism (1998). PMID: 9467534