MK-677 (Ibutamoren) — complete EU guide.
MK-677, also known as Ibutamoren, is an orally active ghrelin-receptor agonist studied for its ability to raise growth hormone and IGF-1 without injections. Despite being sold alongside research peptides, it is chemically a small molecule, not a peptide.
- Non-peptide small molecule (C27H36N4O5S) that activates the ghrelin receptor (GHSR-1a) — grouped with peptide GH secretagogues for its mechanism, not its chemistry.
- Best-replicated finding: a 2-year randomised trial in 65 healthy older adults raised GH/IGF-1 to young-adult levels and increased fat-free mass versus placebo.
- Also increases slow-wave sleep depth and appetite, both linked to its ghrelin-mimetic action.
- Substantial controlled-trial record from 1996–2008 but never reached an approved therapeutic indication anywhere.
- Prohibited under WADA section S2 (peptide hormones, growth factors and mimetics) — banned in and out of competition.
What is MK-677?
MK-677 (Ibutamoren, also coded MK-0677 or L-163,191) is an orally active, non-peptide small molecule developed by Merck in the 1990s. Chemically it is a spiropiperidine compound, structurally closer to a conventional drug than to injectable GH secretagogue peptides such as sermorelin or ipamorelin. It is grouped in this encyclopedia's growth hormone axis category for its mechanism, not its chemistry — it is not a peptide.
How does it work?
MK-677 is a selective agonist of the ghrelin receptor (GHSR-1a), the same receptor targeted by injectable GH secretagogue peptides. By binding this receptor in the hypothalamus and anterior pituitary, it triggers a pulsatile release of growth hormone, which in turn raises IGF-1 in the liver. Because it is orally bioavailable and long-acting, a single daily dose keeps IGF-1 elevated for up to 24 hours — unlike short-acting injectable secretagogues.
What does the research show?
MK-677 has one of the more substantial human trial records among GH secretagogues, running from the mid-1990s through the mid-2000s. Randomised, placebo-controlled trials in healthy older adults, obese men and hip-fracture patients consistently show sustained GH and IGF-1 elevation, increased fat-free mass and improved slow-wave sleep. It did not, however, reach an approved indication in any major market, and functional benefits such as strength and mobility were less consistent than the hormonal and body-composition findings.
EU legal status
MK-677 is not an approved medicine anywhere in the EU and has no recognised medical indication. It is sold by EU research-chemical suppliers as a laboratory reagent, research use only. It is prohibited by WADA under section S2, and its long-acting elevation of GH and IGF-1 makes it detectable well beyond the dosing window in anti-doping testing.
Molecular information
Pharmacokinetics
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Frequently asked questions
Is MK-677 a peptide? ▾
No. Despite being sold and discussed alongside research peptides, MK-677 (Ibutamoren) is a non-peptide small molecule — a spiropiperidine compound. It shares a receptor target (the ghrelin receptor) with peptide GH secretagogues, which is why it is grouped in the same category.
What does MK-677 do? ▾
It binds the ghrelin receptor (GHSR-1a) in the hypothalamus and pituitary, triggering pulsatile growth hormone release and sustained IGF-1 elevation. Human trials also show increased appetite and deeper slow-wave sleep.
Is MK-677 approved as a medicine? ▾
No. It has never received regulatory approval in the EU, US or elsewhere, despite a substantial clinical-trial record from the 1990s and 2000s.
Is MK-677 banned in sport? ▾
Yes. WADA prohibits it under section S2 as a peptide hormone/growth factor mimetic, both in and out of competition.
Does MK-677 affect blood sugar? ▾
Human studies consistently report increases in fasting glucose and reduced insulin sensitivity with sustained use — a mechanistic consequence of chronically elevated GH, not an isolated side effect.
How is MK-677 taken in research settings? ▾
It is orally bioavailable, unlike injectable GH secretagogue peptides. Research suppliers sell it as capsules or a liquid solution, strictly for laboratory research — not for human consumption.
How do I verify MK-677 quality? ▾
Require a batch-specific COA from a named third-party lab confirming identity by mass spectrometry and purity by HPLC (≥98%).
References
- Daily oral MK-677 stimulated the GH-IGF-1 axis in healthy elderly subjects over one month. Chapman IM, et al. J Clin Endocrinol Metab. 1996;81(12):4249–4257. DOI
- Two-year randomised trial: MK-677 raised GH/IGF-1 to young-adult levels and increased fat-free mass in 65 healthy older adults without serious adverse effects. Nass R, et al. Ann Intern Med. 2008;149(9):601–611. DOI PMC2757071
- Randomised crossover study showing MK-677 reversed diet-induced protein catabolism in healthy volunteers. Murphy MG, et al. J Clin Endocrinol Metab. 1998;83(2):320–325. DOI PubMed 9467534