Educational reference, not medical advice. This page summarizes information from published research and regulatory filings for educational purposes. It is not a recommendation to use any compound and should not replace guidance from a licensed healthcare provider. Most peptides discussed here are not approved for the uses described.
What it is
MK-677 — also called ibutamoren or MK-0677 — is a small-molecule (not a peptide) growth hormone secretagogue. It is orally bioavailable, which is the property that distinguishes it from the rest of this category. Despite the structural difference, it acts on the same receptor as ghrelin and the GHRPs — the GHSR-1a — and reproduces the GH and IGF-1 elevation profile of those peptides through a route that does not require injection.
Although it is grouped in the "peptide" reference category for practical reasons, MK-677 is technically a spiroindane spiropiperidine — a small molecule designed by medicinal chemists at Merck to mimic the binding mode of GHRP-6 at the ghrelin receptor.
History
Merck Research Laboratories synthesized MK-677 in the early 1990s as part of an effort to find an orally active small molecule that could replace injectable growth hormone in elderly and frail patients. The 1995 Patchett et al. PNAS paper described the medicinal-chemistry rationale and the early pharmacology.
Merck advanced MK-677 through Phase I and Phase II studies in healthy elderly adults, demonstrating that once-daily oral dosing produced sustained elevation of GH and IGF-1 with effects on body composition. A Phase III program for sarcopenia and frailty in elderly adults was initiated but ultimately did not produce a regulatory submission — published reports cite a lack of functional benefit (strength and physical performance did not improve in line with the body-composition changes) and concerns over fluid retention, insulin sensitivity, and edema as reasons for halting development.
The 2008 Nass et al. paper in Annals of Internal Medicine reported the most thorough efficacy and safety data — a 2-year trial in 65 healthy older adults showing increased fat-free mass and IGF-1, but no significant improvement in strength or function.
Regulatory status
MK-677 has never been approved by any regulator. The FDA has not approved it; it is not on the 503A bulk substances list and compounding pharmacies in the United States are not permitted to prepare it for patients. The European Medicines Agency has not authorized it.
The World Anti-Doping Agency lists MK-677 under class S2 of the Prohibited List (peptide hormones, growth factors, related substances, and mimetics) — banned in and out of competition.
MK-677 is widely sold online as a "research chemical" and is frequently mislabeled as a "SARM" — selective androgen receptor modulator — which it is not. It has no androgen receptor activity.
How researchers describe its action
Published mechanism papers describe MK-677 as an orally bioavailable agonist of the ghrelin/GHSR-1a receptor. Receptor activation on pituitary somatotrophs raises intracellular calcium and stimulates growth hormone release; activation on hypothalamic neurons amplifies endogenous GHRH release and reduces somatostatin tone, increasing the GH pulse.
Unlike injectable peptides with short half-lives, MK-677 produces sustained receptor occupancy over 24 hours — meaning GH and IGF-1 remain elevated continuously rather than in discrete pulses. In the Nass trial, IGF-1 rose by roughly 40% over baseline and remained elevated throughout the study.
Cortisol increased modestly in the published trials; prolactin was largely unchanged.
Half-life and dosing intervals
The published plasma half-life of MK-677 is approximately 24 hours, which is the basis for once-daily oral dosing. Steady-state IGF-1 levels are reached after roughly 1 to 2 weeks of consistent dosing.
In the Nass et al. 2-year trial, the dose was 25 mg orally once daily. Earlier Phase II studies used 10 or 25 mg daily and showed dose-dependent IGF-1 elevation. Doses above 25 mg did not produce proportional additional benefit and increased side effect rates.
Reconstitution example
MK-677 is an orally bioavailable small molecule and is not reconstituted from a lyophilized vial — it is supplied as capsules, oral solution, or oral powder. Where it is sold as a research powder in 10 mg or 25 mg increments, dosing is typically managed by milligram weight per capsule rather than by syringe.
For a 25 mg capsule once daily, the total daily intake matches the dose used in the Nass et al. trial. A 10 mg capsule once daily corresponds to the lower dose tested in earlier Phase II work. Vial's tracking tools accept oral mg input directly when the route is set to oral.
What to know
- Not a peptide. MK-677 is a small molecule, included in this reference set because it activates the same receptor as the peptide GHRPs and is commonly grouped with them.
- Not approved. Phase III development was halted; no regulator has authorized MK-677 for therapeutic use, and it is not eligible for compounding in the United States.
- WADA banned. Use is prohibited in competitive sport.
- Mislabeled online. MK-677 is frequently sold as a "SARM" but has no androgen receptor activity.
- Reported side effects in the Nass and earlier Phase II trials: increased appetite (consistent with ghrelin-receptor activity), fluid retention and edema, lethargy, transient elevation in fasting glucose and reduction in insulin sensitivity, and transient muscle pain. Worsening of congestive heart failure was observed in one elderly subgroup study.
- Storage. Capsules and powder should be stored at room temperature, protected from light and moisture, per typical supplier guidance.
Sources
- 1.Nass R et al. (2008). Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Annals of Internal Medicine.
- 2.Patchett AA et al. (1995). Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue. Proceedings of the National Academy of Sciences USA.
- 3.Smith RG et al. (2001). Growth hormone secretagogue receptor family members and ligands. Endocrine.
- 4.Sigalos JT, Pastuszak AW (2018). The Safety and Efficacy of Growth Hormone Secretagogues. Sexual Medicine Reviews.
- 5.World Anti-Doping Agency — Prohibited List (S2).