“Acetamoren” or “MK-777” is a name used by online sellers for a compound they market as a newer, longer-acting version of ibutamoren (MK-677), the oral growth hormone secretagogue (a drug that makes the pituitary release more growth hormone). It is sold as a “research chemical” for the same uses as ibutamoren: muscle gain, recovery and sleep.
The single most important fact: no primary source identifies a drug called acetamoren or MK-777. The name does not appear in PubMed, PubChem, FDA’s substance registry or the WADA Prohibited List. No company has published a study of it, and no human or animal data exist under this name. The Merck code it resembles, MK-0777, belongs to an unrelated brain-acting drug candidate that works on GABA-A receptors (see below).
This page summarizes what chemical registries and the scientific literature show, and where the trail ends. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| What sellers call it | Acetamoren, MK-777; marketed as a successor to ibutamoren (MK-677) |
| Identity in registries | Not listed under either name; the CAS number some sellers give (950841-87-9) belongs to N-acetyl ibutamoren |
| Relation to ibutamoren | If the seller CAS is correct: ibutamoren with an acetyl group on its free amino group |
| Route | Marketed by sellers as oral; no approved or studied formulation |
| Studied doses | None; no published human or animal study |
| Half-life | Not reported in any published study |
| FDA status | Not approved; no FDA application or review found |
| US controlled substance | Not named in Schedule III (21 CFR 1308.13) |
| WADA status | Not named; S2 bans growth hormone secretagogues and substances with similar structure or effect |
What it is
What the registries show
Searches of PubMed and PubChem for “acetamoren,” “MK-777” and “MK777” return no records (PubChem). Neither name is an international nonproprietary name, and no company or university has published under either code.
Some seller pages give a CAS registry number, 950841-87-9. In PubChem that number belongs to a compound titled N-acetyl ibutamorelin, formula C₂₉H₃₈N₄O₆S, molecular weight 570.7 g/mol (PubChem CID 57595228). FDA’s Global Substance Registration System lists the same structure as N-acetyl ibutamorelin (UNII DHZ77GVH76), with a mesylate salt as a related substance (FDA GSRS). Neither registry uses the name acetamoren or MK-777, and neither links the structure to any published pharmacology.
Other seller pages give a different CAS number, 1797406-69-9. PubChem assigns that number to MZ1, a large research molecule unrelated to growth hormone (PubChem CID 122201421). This mismatch is one more sign that the product’s identity is not fixed.
How N-acetyl ibutamoren differs from ibutamoren
Comparing the PubChem records, the two structures are the same except at one position:
| Compound | PubChem name (key part) | Formula | Molecular weight |
|---|---|---|---|
| Ibutamoren (CID 178024) | 2-amino-2-methyl-N-… | C₂₇H₃₆N₄O₅S | 528.7 g/mol |
| N-acetyl ibutamoren (CID 57595228) | 2-acetamido-2-methyl-N-… | C₂₉H₃₈N₄O₆S | 570.7 g/mol |
In other words, an acetyl group is attached to ibutamoren’s free amino group. No published study reports whether this changes how the molecule binds the ghrelin receptor, how well it is absorbed, or how long it lasts. Claims that it is “stronger,” “longer-acting” or “easier on blood sugar” than ibutamoren have no traceable source.
There is also no independent evidence that products sold as acetamoren actually contain N-acetyl ibutamoren. The CAS link comes from sellers, not from a regulator, a manufacturer’s filing or a laboratory analysis.
The real MK-0777
Merck’s own publications give ibutamoren’s code as MK-0677 (L-163,191) (Patchett et al., PNAS 1995). The code MK-0777 was assigned to a different Merck compound, TPA023 (also L-830,982), a triazolopyridazine (PubChem CID 9908684). It binds the benzodiazepine site of GABA-A receptors, the brain’s main inhibitory receptors, and acts as a partial agonist at the α2 and α3 subtypes only. In humans, a single 2 mg dose occupied about 50–60% of these sites without obvious sedation (Atack et al., JPET 2010).
MK-0777 was tested in people with schizophrenia to see if it improved thinking and memory:
| Trial | Design | Result |
|---|---|---|
| Lewis et al., Am J Psychiatry 2008 | 15 men with chronic schizophrenia; MK-0777 or placebo for 4 weeks | Better scores on several working-memory tasks; well tolerated |
| Buchanan et al., Biol Psychiatry 2011 | 60 people; 3 mg or 8 mg twice daily, or placebo, for 4 weeks | No benefit on the primary cognitive score; authors concluded “little benefit” |
MK-0777 has nothing to do with growth hormone. Its only link to “MK-777” is the similar code.
About the “MK-777” name. The label borrows the format of Merck research codes and adds 100 to MK-677, which makes it sound like an official follow-up drug. We found no Merck publication or clinical trial for a growth hormone secretagogue called MK-777.
Pharmacokinetics
No pharmacokinetic data exist for acetamoren or for N-acetyl ibutamoren. No study reports its absorption, half-life, metabolism or duration of action, in people or in animals. Any half-life quoted for it, including figures of around 20 hours, is not supported by a published measurement.
For the parent compound, the human pharmacokinetic record is also thin. See the ibutamoren page for what is known.
Regulatory status
- FDA. No drug containing acetamoren or N-acetyl ibutamoren has been approved, and we found no FDA review, warning letter or compounding evaluation that names it. FDA’s registry lists the structure only as an identified substance (FDA GSRS).
- DEA. It is not named among the Schedule III anabolic steroids or other substances (21 CFR 1308.13).
- Sport. The WADA 2026 list does not name acetamoren or MK-777. However, section S2 bans growth hormone secretagogues “and their mimetics,” with ibutamoren (MK-677) as a named example, plus “other substances with similar chemical structure or similar biological effect(s).” It is prohibited at all times, as a non-specified substance. Section S0 also bans any pharmacological substance with no current approval for human therapeutic use (WADA 2026 Prohibited List). An athlete could not rely on the absence of the name.
What the research shows
There is no research on acetamoren. No randomized trial, case series, animal study or laboratory binding study has been published under this name or for N-acetyl ibutamoren.
All of the effects claimed for it are borrowed from ibutamoren. Ibutamoren itself raised growth hormone and IGF-1 in trials and added modest lean mass in older adults, but did not improve strength or function, and it consistently raised blood sugar. Those results are covered on the ibutamoren page. They cannot be assumed to apply to a different molecule, or to a product whose contents are unverified.
Side effects and risks
Unknown safety profile
No safety data exist. Nobody has published how acetamoren affects blood sugar, blood pressure, the heart or the liver, or what doses are toxic.
Risks if it acts like ibutamoren
If the product does stimulate the ghrelin receptor as sellers claim, the known risks of ibutamoren would be a reasonable concern. These include higher blood sugar and insulin resistance, fluid retention, increased appetite, and a heart failure signal in frail older patients. Details and trial rates are on the ibutamoren page.
Unknown contents
Because the compound has no confirmed identity, there is no reference standard to test a product against. Sellers do not agree on its CAS number, and one of the numbers they use belongs to an unrelated molecule. A buyer has no reliable way to know what a product contains or how much.
Key takeaways
- No primary source defines it. “Acetamoren” and “MK-777” do not appear in PubMed, PubChem, FDA’s registry or the WADA list.
- Possibly N-acetyl ibutamoren. One seller-supplied CAS number points to ibutamoren with an acetyl group added, but no regulator or lab analysis confirms that products contain it.
- The real MK-0777 is unrelated. Merck’s MK-0777 (TPA023) is a GABA-A drug tested for schizophrenia, not a growth hormone secretagogue.
- No studies, no dosing, no half-life. There are no human or animal data, so every claimed benefit and kinetic figure is borrowed from ibutamoren or unsupported.
- Banned in sport by class. WADA’s S2 and S0 sections cover growth hormone secretagogues, related structures and unapproved substances, even when unnamed.
Sources
- 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):7001–7005. PubMed.
- National Center for Biotechnology Information. N-Acetyl Ibutamorelin, PubChem CID 57595228. PubChem.
- Food and Drug Administration. Global Substance Registration System: N-Acetyl Ibutamorelin, UNII DHZ77GVH76. FDA GSRS.
- National Center for Biotechnology Information. Ibutamoren, PubChem CID 178024. PubChem.
- National Center for Biotechnology Information. MZ1, PubChem CID 122201421. PubChem.
- National Center for Biotechnology Information. TPA023 (MK-0777), PubChem CID 9908684. PubChem.
- Atack JR, Wong DF, Fryer TD, et al. Benzodiazepine binding site occupancy by the novel GABAA receptor subtype-selective drug 7-(1,1-dimethylethyl)-6-(2-ethyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2-fluorophenyl)-1,2,4-triazolo[4,3-b]pyridazine (TPA023) in rats, primates, and humans. J Pharmacol Exp Ther. 2010;332(1):17–25. PubMed.
- Lewis DA, Cho RY, Carter CS, et al. Subunit-selective modulation of GABA type A receptor neurotransmission and cognition in schizophrenia. Am J Psychiatry. 2008;165(12):1585–1593. PubMed.
- Buchanan RW, Keefe RS, Lieberman JA, et al. A randomized clinical trial of MK-0777 for the treatment of cognitive impairments in people with schizophrenia. Biol Psychiatry. 2011;69(5):442–449. PubMed.
- World Anti-Doping Agency. The 2026 Prohibited List, in effect January 1, 2026. WADA 2026 Prohibited List.
- Code of Federal Regulations. 21 CFR 1308.13, Schedule III. 21 CFR 1308.13.
- National Center for Biotechnology Information. PubChem search portal. PubChem.