MK-677 (Ibutamoren) (10mg/capsule) 60 Capsules

MK-677, also called ibutamoren, is a small synthetic molecule that activates GHS-R1a, the ghrelin receptor. It is not a peptide, although it is usually sold alongside the peptide growth hormone secretagogues. This listing is a sealed bottle of 60 hard gelatin capsules, each labelled to hold 10 mg of ibutamoren blended with microcrystalline cellulose. Research on the compound covers its design at Merck, the receptor it acts on and a set of controlled human studies of the growth hormone axis.

Specifications

What is in each capsule

The safety data sheet lists 10 mg of ibutamoren per capsule, about 2.5% of the capsule contents by weight, with microcrystalline cellulose as the filler and a gelatin shell. It describes the active ingredient as ibutamoren mesylate, the salt used in the clinical trials and the form in which the compound is commonly supplied. As a pure substance ibutamoren is classified as toxic if swallowed (H301), which is one reason the capsules are handled as a laboratory chemical and not as anything resembling a supplement.

The bottle is kept at room temperature, 15 to 25 °C, tightly closed in its original container and away from light and moisture. It needs no refrigeration.

Not a peptide, and not a SARM

Ibutamoren is a spiroindoline sulfonamide, with no amino acids and no peptide bonds. Merck set out to make a small molecule that would act like the growth hormone releasing peptides while having the pharmacokinetics of a conventional drug. In the 1995 paper that introduced it under the code L-163,191, it released growth hormone from cultured rat pituitary cells in the low nanomolar range and was mechanistically indistinguishable from GHRP-6¹.

Nor is it a selective androgen receptor modulator, though it is often shelved next to them. SARMs bind the androgen receptor, a nuclear receptor that changes which genes a cell transcribes. Ibutamoren’s target is a G-protein-coupled receptor, the same one GHRP-6 and ipamorelin act on. The guide to SARMs versus peptides sets out how the classes differ.

What the research covers

The receptor it acts on

A year after ibutamoren was described, Howard and colleagues cloned its target, a G-protein-coupled receptor found in the pituitary and in the arcuate and infundibular hypothalamus of pigs and humans². They wrote that synthetic secretagogues stimulate and amplify pulsatile growth hormone release through it, and took the receptor as a sign of a natural hormone that had not yet been found². That hormone turned out to be ghrelin, and GHS-R1a is now known as the ghrelin receptor.

Controlled studies in people

Ibutamoren has a longer human trial record than most compounds sold for research. In a randomised, placebo-controlled study of 32 healthy adults aged 64 to 81, blood drawn every 20 minutes over 24 hours showed growth hormone rising through taller pulses and higher troughs, with no change in the number of pulses³. Serum IGF-I climbed into the range seen in young adults, and fasting glucose rose too³. A two-year randomised, placebo-controlled trial in 65 healthy adults aged 60 to 81 later set fat-free mass and abdominal visceral fat as its primary end points⁴. Fat-free mass increased against placebo, visceral and total fat did not differ, and strength and function did not change⁴. Fasting glucose and cortisol went up, insulin sensitivity went down, and the commonest side effects were increased appetite, mild swelling of the lower legs and muscle pain⁴. The authors judged the trial too small and too short to assess functional outcomes⁴.

What the record does not show

These were studies of the growth hormone axis in healthy volunteers, mostly small, and none used material from a research supplier. The MK-677 (ibutamoren) guide covers the rest of the trial record, including a hip-fracture trial stopped early for a heart-failure safety signal. It also covers the compound’s legal position: never approved for human use anywhere, ruled by the FDA to fall outside the dietary supplement definition, and prohibited by WADA.

How each lot is tested

Every lot is tested in PrymaLab’s own laboratory in Ashland, Kentucky before release. Published certificates are listed on the results page and can be checked by number and key on the verify page. These are in-house results from PrymaLab Analytical, not an independent test, and the lab is not accredited to ISO 17025. The third-party testing guarantee on this page still applies: if any independent laboratory finds the wrong compound, or less than the stated purity or amount, the order is refunded and the cost of the test is reimbursed.

Frequently asked questions

References

1. Patchett AA, Nargund RP, Tata JR, et al. Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue. Proc Natl Acad Sci U S A. 1995;92(15):7001-5. DOI · PubMed
2. Howard AD, Feighner SD, Cully DF, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996;273(5277):974-7. DOI · PubMed
3. Chapman IM, Bach MA, Van Cauter E, et al. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab. 1996;81(12):4249-57. DOI · PubMed
4. Nass R, Pezzoli SS, Oliveri MC, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med. 2008;149(9):601-11. DOI · PubMed