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hormone

MK-677

Also known as: Ibutamoren, Ibutamoren mesylate, MK-0677, L-163191
Moderate evidence FDA: research-only WADA: Prohibited at all times

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
02

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.

03

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.

04

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 research-only
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. 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).