MK-777 (Acetamoren): Chemical Identity, Proposed Mechanism and the Evidence Gap

For laboratory research use only. Not for human consumption. All compounds referenced in this article are sold by Explicit SARMs solely as reference materials for in-vitro and animal research by qualified professionals. Nothing here is medical advice, and no statement has been evaluated by the FDA. These materials are not intended to diagnose, treat, cure or prevent any disease.

MK-777, sold under the name acetamoren, is one of the newer compounds to appear in research chemical catalogs. It is generally presented as a relative or successor of MK-677 (ibutamoren), the well-studied nonpeptide ghrelin-receptor agonist. Because the name sounds like a pharmaceutical development code, it is easy to assume a body of published research sits behind it. That is not the case, and any responsible research summary has to start there.

This article sets out what can actually be verified about MK-777: its reported chemical identity, how that structure relates to ibutamoren, what mechanism is proposed, where the evidence stops, and what that means for laboratories that want to study it. Explicit SARMs supplies MK-777 Acetamoren Capsules strictly as laboratory reference material.

What Is MK-777?

Chemical registry listings associate the name acetamoren, and the synonym MK777, with CAS number 950841-87-9, molecular formula C29H38N4O6S and a molecular weight of about 570.7. [1] The systematic name given in those listings describes a 2-(acetylamino)-2-methylpropanamide attached to the same spiro-indoline-piperidine and benzyloxymethyl framework found in ibutamoren.

Comparing that with ibutamoren itself is instructive. PubChem lists ibutamoren (CID 178024) with formula C27H36N4O5S, molecular weight 528.7, and a 2-amino-2-methylpropanamide group in the same position. [2] The difference between the two formulas, C2H2O, corresponds exactly to an acetyl group. In other words, the registered structure for acetamoren is the N-acetyl derivative of ibutamoren: the free amino group of ibutamoren is capped as an acetamide.

• Common names: MK-777, MK777, acetamoren
• Reported CAS: 950841-87-9
• Reported formula and molecular weight: C29H38N4O6S, about 570.7
• Structural relationship: N-acetyl derivative of ibutamoren (MK-677)
• Proposed class: nonpeptide growth hormone secretagogue (ghrelin-receptor agonist)
• Not a SARM; no androgen receptor activity has been reported or proposed
• Regulatory status: not approved by the FDA or any other regulator; no registered clinical trials

Is MK-777 a Merck Compound?

There is no public evidence that it is. “MK” is the prefix Merck uses for internal development compounds, and MK-0677 is a genuine Merck designation with a 1995 publication describing its design. [4] For MK-777, we found no Merck publication, no patent assigned under that code, and no registered trial. A PubMed search in October 2026 returned zero records for “MK-777”, “MK777”, “acetamoren” or the CAS number, and ClinicalTrials.gov returned no studies under the name. [3] The name appears to be a commercial designation rather than a pharmaceutical development code. Independent reviewers have reached the same conclusion. [8]

Proposed Mechanism of Action

MK-777 is marketed as an agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the receptor activated by ghrelin and by ibutamoren. [5] Given the close structural relationship to ibutamoren, that is a reasonable hypothesis, but it is a hypothesis.

Medicinal chemistry gives reasons to be cautious about assuming the two compounds behave the same way:

• The free amine is part of the pharmacophore. In the Merck GHS series, the basic amino group of the aminoisobutyric acid side chain is a recognized feature of the ligand. Converting it to a neutral acetamide removes its basicity and could change receptor binding, potency or efficacy in either direction.
• Prodrug possibility. An N-acetyl group can be removed by amidases in vivo. If that happens, some activity attributed to MK-777 in animal models could come from ibutamoren formed by metabolism. Only pharmacokinetic and metabolite studies can answer this.
• Physicochemical changes. Acetylation changes polarity, solubility and membrane permeability, which can affect absorption and tissue distribution.

None of these questions has been answered in published, peer-reviewed work.

Research History

There is no traceable research history in the scientific literature. MK-777 entered the research chemical market in the mid-2020s with commercial descriptions that claim advantages over MK-677, such as greater receptor selectivity or different effects on appetite and glucose. We could not find any primary data supporting those claims, and a recent comparative review of MK-677 and MK-777 concluded that the claimed advantages remain unsubstantiated. [8]

What Published Studies Report

On MK-777 itself

No peer-reviewed receptor-binding, functional, pharmacokinetic, animal or human studies on MK-777 or acetamoren could be located. [3]

On the parent compound

The best available reference point is ibutamoren. Its published record includes the original design paper, its role in cloning the ghrelin receptor, and multiple clinical trials. [4][5] Those trials reported consistent increases in GH and IGF-1 alongside safety-relevant findings such as increased fasting glucose, reduced insulin sensitivity and increased cortisol, and a congestive heart failure safety signal that ended a hip fracture trial early. [6][7] Those findings belong to ibutamoren. They cannot be transferred to MK-777 without data, but they define the endpoints any MK-777 study should measure.

Research Considerations

Because the evidence base is empty, characterization work is the most valuable research that can be done on MK-777:

• Confirm identity first. Use LC-MS and, ideally, NMR to confirm that the material matches the registered N-acetyl structure (expected monoisotopic mass about 570.25 Da) and is not ibutamoren or a mixture.
• Quantify residual ibutamoren. Because acetamoren is an ibutamoren derivative, ibutamoren is a plausible synthetic impurity or degradant. HPLC methods should resolve and quantify it.
• Receptor pharmacology. Run GHS-R1a binding and functional assays side by side with an ibutamoren reference standard.
• Metabolic stability. In-vitro liver microsome or plasma stability studies can test whether the acetyl group is cleaved to release ibutamoren.
• Endpoints in animal work. Mirror the ibutamoren literature: GH pulsatility, IGF-1, food intake, glucose and insulin, and cortisol.

Evaluating Claims About New Compounds

MK-777 is a useful example of how to assess any research chemical marketed as a successor to a known molecule. A practical checklist:

• Is there a published structure? For MK-777, a registry structure exists, which is a starting point. [1]
• Is there a primary pharmacology paper? Binding affinity, functional potency and selectivity should be reported in a peer-reviewed source. For MK-777, none was found. [3]
• Is there a patent or originator? Pharmaceutical development codes usually trace to a company and a patent family. No such trail was found for MK-777.
• Are there registered trials? ClinicalTrials.gov returned none. [3]
• Do claimed advantages cite data? Claims of improved selectivity or reduced side effects should point to comparative studies. They currently do not. [8]

Until those gaps are filled, MK-777 is best treated as an uncharacterized analog of ibutamoren, and research on it as early-stage characterization work.

WADA Status

MK-777 is not named on the WADA Prohibited List. However, section S2.2.4 prohibits growth hormone secretagogues and their mimetics “including, but not limited to” the named examples, which include ibutamoren. [9] A compound marketed as a GHS-R1a agonist would fall within that class description.

Storage, Purity and COA

• Store capsules sealed, dry and away from light and heat.
• Log lot numbers and receipt dates with every experiment.
• For a compound with no literature, the Certificate of Analysis carries more weight than usual. A useful COA reports HPLC purity, confirms identity by mass spectrometry against the expected mass, and ideally reports ibutamoren content.

For lot documentation, use the contact page.

Related Research Compounds

• Ibutamoren MK-677 Capsules, the parent compound and the natural reference standard
• MK-677 Liquid, the same parent compound in solution
• Ipamorelin 5mg, a peptide agonist at the same receptor
• SARMs collection

Frequently Asked Questions

What is MK-777?

MK-777, or acetamoren, is a research chemical whose registered structure is the N-acetyl derivative of ibutamoren (MK-677). It is marketed as a ghrelin-receptor agonist. [1][2]

Is MK-777 a SARM?

No. It is proposed to act on the ghrelin receptor, not the androgen receptor.

Is MK-777 the same as MK-677?

No. They are structurally related but distinct molecules with different formulas and molecular weights. Whether they share the same pharmacology has not been tested in published research.

Are there published studies on MK-777?

Not that we could find. PubMed and ClinicalTrials.gov returned no records for MK-777 or acetamoren as of October 2026. [3]

Is MK-777 approved by the FDA?

No. It has never been approved by the FDA or any other regulator and has no registered clinical trials.

Is MK-777 prohibited in sport?

It is not named on the WADA list, but growth hormone secretagogues and their mimetics are prohibited as a class under S2.2.4. [9]

References

1. ChemicalBook. Acetamoren (MK777), CAS 950841-87-9: basic information and chemical properties. chemicalbook.com
2. PubChem. Ibutamoren, CID 178024. pubchem.ncbi.nlm.nih.gov
3. Searches performed October 2026: PubMed “acetamoren” and ClinicalTrials.gov “MK-777” (no records)
4. Patchett AA, 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. PubMed 7624358
5. Howard AD, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996. PubMed 8688086
6. Nass R, 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. PubMed 18981485
7. Adunsky A, et al. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Arch Gerontol Geriatr. 2011. PubMed 21067829
8. Moazzeni B. MK-677 Versus MK-777: A Comparative Review of Growth Hormone Secretagogues, Receptor Pharmacology, Metabolic Effects, and Translational Drug Development. ResearchGate preprint. researchgate.net
9. World Anti-Doping Agency. 2026 Prohibited List. wada-ama.org

For laboratory research use only. Not for human consumption. All compounds referenced in this article are sold by Explicit SARMs solely as reference materials for in-vitro and animal research by qualified professionals. Nothing here is medical advice, and no statement has been evaluated by the FDA. These materials are not intended to diagnose, treat, cure or prevent any disease.