MK-677

Last Updated: August 2026

MK-677 (INN Ibutamoren; developmental codes MK-0677, L-163,191) is an orally active, long-acting, non-peptide agonist of the ghrelin receptor (GHSR-1a) and a growth hormone secretagogue, developed by Merck & Co. It mimics the GH-stimulating action of ghrelin, raising growth hormone and IGF-1 while preserving the body's natural pulsatile rhythm. It is not a peptide (it's a spiroindoline small molecule) and not a SARM (it does not act on androgen receptors) — it is frequently mislabeled as both. It is not approved for any indication and is supplied for research use only.

What is MK-677 and how does the ghrelin/GH mechanism work?

MK-677 binds GHSR-1a in the hypothalamus and pituitary with sub-nanomolar affinity (Ki ~0.4 nM), reinforcing GHRH signaling and dampening somatostatin, which raises GH output — and, downstream, hepatic IGF-1 — for up to 24 hours from a single oral dose. Unlike injected GH, it acts upstream on the neuroendocrine axis rather than flooding the system with exogenous hormone, and unlike injectable secretagogues such as Ipamorelin or CJC-1295, it is orally bioavailable (~60–70%). That oral, once-daily profile is its main point of differentiation in GH research.

What does the clinical evidence show?

MK-677 robustly and reproducibly raises GH and IGF-1 in humans across multiple controlled studies — for example, a 2-year randomized, placebo-controlled trial of oral MK-677 in healthy older adults sustained elevated GH and IGF-1 and increased fat-free mass, though without demonstrated functional benefit1 source — but elevating those markers has not translated into an approved therapeutic indication. Trials have examined it in healthy older adults, GH-deficient patients, and catabolic states, and a large Alzheimer's program (as MK-0677) did not demonstrate clinical benefit. Evidence level: Human RCTs on surrogate endpoints (GH/IGF-1, body composition); not approved. Its effect on appetite is pronounced — like ghrelin, it increases hunger.

Is MK-677 a SARM or a steroid?

No — MK-677 is a non-peptide ghrelin-receptor agonist / GH secretagogue, mechanistically unrelated to SARMs and anabolic steroids. It gets grouped with SARMs because it's sold on the same bodybuilding vendor sites and stacked with them, but it does not bind androgen receptors — see peptides vs SARMs vs steroids for how the three classes differ. Functionally it belongs with GH secretagogues like the GHRPs and Ipamorelin — it's simply the orally active small-molecule version.

What are the documented side effects of MK-677?

The best-documented effects are increased appetite, water retention/edema, and reductions in insulin sensitivity with raised fasting glucose — consequences of sustained GH/IGF-1 elevation. Lethargy and transient increases in blood pressure have also been reported. Beyond metabolic effects, the sustained rise in GH/IGF-1 and the compound's fluid-retaining effect raise cardiovascular questions: a Phase IIb trial of MK-0677 in older adults recovering from hip fracture was terminated early because of a congestive-heart-failure safety signal, and the investigators concluded it had an unfavorable safety profile in that population.1 source The insulin-sensitivity signal is the most clinically relevant and is a reason its development stalled. Evidence level: Human RCT. Not a self-administration recommendation.

What is the regulatory status of MK-677?

MK-677 is an investigational compound not approved by the FDA or any regulator for any indication, and it is not available by prescription. Its salt, ibutamoren mesylate, does appear on the FDA's Category 2 list of bulk drug substances that "may present significant safety risks" when used in compounding — flagged for both 503A pharmacy compounding and 503B outsourcing-facility routes. That is the opposite of an approval: the FDA has identified it as a compounding safety concern, and it remains one of only five peptides/peptide-adjacent substances on the active Category 2 list (with GHRP-2, GHRP-6, ipamorelin acetate, and kisspeptin-10), as of August 2026.1 source It circulates as a research chemical. It is also a prohibited in sport at all times — the WADA 2026 Prohibited List names "ibutamoren (MK-677)" by example under S2.2.4 (growth hormone secretagogues), within S2.2 Peptide Hormones and their Releasing Factors (as of August 2026)1 source. Verify local rules via the legal status guide.

Why does vendor verification matter, and how does Peptigrity verify?

As a cheap-to-counterfeit oral compound sold widely in the gray market, MK-677 carries real underdosing and mislabeling risk — independent HPLC and mass-spec (expected MW 528.67) are the objective checks. Peptigrity collects independent third-party Certificates of Analysis for MK-677 from shops' official channels and verifies each for authenticity before publishing. Because shops choose which COAs to publish, results reflect the batches shops have made public rather than every production batch — a selection bias we state openly. A community-funded Testing Grant to purchase and test vials anonymously is in development. Tests in the database come from independent labs such as Janoshik Analytical, Freedom Diagnostics, and Chromate; the trust score weights independent lab purity and community reviews equally (50/50). See the independent MK-677 lab tests on file and how to read lab results.

Educational information only; not medical advice. MK-677 is an investigational compound not approved by the FDA or any regulator. Consult a qualified healthcare provider before using any research compound. Peptigrity does not sell, endorse, or recommend products or vendors.