MK-677 (Ibutamoren) Capsules
A bottle of 60 hard gelatin capsules with 10 mg each of a non-peptide small molecule that activates the ghrelin receptor. Each lot is tested in the manufacturer’s own laboratory. Laboratory research use only, not for consumption.
| Compound | Ibutamoren (MK-677), ghrelin receptor agonist (mesylate as commonly supplied) |
|---|---|
| CAS number | 159752-10-0 |
| Molecular formula | C27H36N4O5S |
| Contents | MK-677: 10 mg per capsule |
| Form | Hard gelatin capsules containing the active substance blended with microcrystalline cellulose, packed in a sealed bottle |
| Storage, sealed | Store at room temperature (15–25 °C) in the tightly closed original container, dry and protected from light |
| Format | Capsules in a sealed bottle |
Sizes and lots
- 10 mg × 60 · 1 bottle — $63.99
- 10 mg × 60 · Kit of 10 — $568.87
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.
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
Frequently asked questions
Is MK-677 a peptide?
No. Ibutamoren is a small synthetic molecule with no amino acids in it. It gets grouped with GHRP-6 and ipamorelin because all three act on the ghrelin receptor, GHS-R1a, but the chemistry is entirely different. It is not a SARM either, since it does not bind the androgen receptor.
What hazards does the safety data sheet list?
It classifies ibutamoren as a pure substance as toxic if swallowed (H301). The cellulose filler and gelatin shell are not classified. The sheet sets out handling, first aid and disposal, and asks for the bottle to stay closed, labelled and out of reach of unauthorised people.
How should the bottle be stored?
At room temperature, 15 to 25 °C, tightly closed in the original container, dry and protected from light. The capsules need neither a refrigerator nor a freezer. Recapping the bottle soon after each opening keeps moisture away from the fill.
Do the human trials mean MK-677 is approved for people?
No. Those were investigational trials, and ibutamoren has never been approved as a medicine in any country. This product is sold only for laboratory research. It is not a dietary supplement and must not be swallowed by, or given to, people or animals.
References
- 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
- 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
- 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
- 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
For laboratory research use only. Not for human or veterinary consumption. Products have not been evaluated by the U.S. Food and Drug Administration and are not intended to diagnose, treat, cure or prevent any disease.