MK-777 (Acetamoren): what the name means and how it relates to MK-677

Searches for "MK 777", "acetamoren" and "acetamoren vs MK677" ask whether this is a new compound, whether it relates to MK-677 and whether anyone has studied it. MK-777, listed as Acetamoren, is Free Muscle's own designation for a product in its Bioreactive Series. Neither name returns a record in PubMed or PubChem, no pharmacology, effect or tolerability data exist under either name, and this article attributes none. Free Muscle sells MK-777 and MK-677 for laboratory research only, to adults aged 18 or over; nothing here is guidance on use.

What is MK-777 (Acetamoren)?

MK-777 and Acetamoren are Free Muscle's designations for a product in its Bioreactive Series, supplied as a bottle of 60 capsules. A product designation is the name a seller gives a product so that it and its batches can be identified within a range. It is not issued by a naming body and does not point to a recorded structure.

A researched compound is different: it carries several names, each tied to a record that can be checked. Ibutamoren was characterised in 1995 by researchers at Merck Research Laboratories under the development codes L-163,191 and MK-0677 (Patchett et al., 1995). PubChem records ibutamoren as its international non-proprietary name (INN), with CAS number 159634-47-6 and record CID 178024 (C27H36N4O5S, molecular weight 528.7); its name lookup for "MK-677" returns the mesylate salt instead (CID 6450830, molecular weight 624.8).

Three things follow for MK-777.

  • There is nothing to look up. The name matches no published structure, paper or trial.
  • The name does not define the contents. The batch certificate of analysis does.
  • Nothing can be borrowed. Statements about what MK-777 does, how long it lasts or what side effects it causes cannot be traced to any published source, so this article makes none.

Acetamoren and MK-777 studies: what PubMed and PubChem return

On 27 September 2026 we ran each name below through PubMed, using the NCBI E-utilities search service, and through the PubChem name lookup.

Name searched PubMed records PubChem record What the name refers to
MK-777 0 None found Free Muscle product designation
MK777 0 None found The same designation without the hyphen
Acetamoren 0 None found Free Muscle's name for the same product
MK 777 (two words) 61, all unrelated None found PubMed matches "MK" and "777" as separate words
MK-0777 29 CID 9908684 (TPA023) An unrelated development compound
MK-677 123 CID 6450830 (mesylate salt) Ibutamoren
Ibutamoren 121 CID 178024 (free base) The non-proprietary name of MK-677

The zeros are the finding. The 61 results for "MK 777" as two words are unrelated papers, on subjects such as electrocardiograms, soil bacteria and COVID-19, that happen to contain both strings.

MK-777 vs MK-677: why the names look alike

The resemblance is in the letters: "MK" plus a number echoes MK-677, the short form of ibutamoren's Merck code, and "Acetamoren" shares ibutamoren's ending. Free Muscle files the product in the MK-677 collection as well as its own MK-777 collection. That shows where it sits in the range, not a shared origin, structure or data.

MK-0777 is a real code for a different molecule

Read the way MK-677 is short for MK-0677, "MK-777" would point to MK-0777, and that code exists. PubChem lists it as a synonym of TPA023 (CID 9908684, C20H22FN7O), a triazolopyridazine unrelated to ibutamoren. The 29 PubMed records retrieved for MK-0777 concern TPA023 and related GABA-A receptor research, not the Free Muscle product.

Acetamoren is not acetaminophen

The shared letters imply no chemical link. Acetaminophen is paracetamol (PubChem CID 1983, C8H9NO2), a common painkiller, and nothing published about it describes MK-777.

MK-677 (ibutamoren): context, not evidence for MK-777

This section describes MK-677 only. None of it describes MK-777 or any product sold here.

In its 1995 design paper, MK-0677 released growth hormone from cultured rat pituitary cells by a mechanism indistinguishable from that of the peptide GHRP-6. Given by mouth to dogs, it raised growth hormone with no significant effect on aldosterone, luteinising hormone, thyroxine or prolactin, and only modest rises in cortisol (Patchett et al., 1995).

A two-year, double-blind trial randomised 65 healthy adults aged 60 to 81 to MK-677 or placebo (Nass et al., 2008). Growth hormone and IGF-1 rose to young-adult levels. Fat-free mass rose by 1.1 kg on MK-677 and fell by 0.5 kg on placebo, with no significant difference in abdominal visceral fat or total fat mass. Body weight and limb fat rose more than on placebo, fasting glucose and cortisol rose, and insulin sensitivity fell. The most frequent side effects were increased appetite, which subsided within a few months, and transient, mild lower-limb swelling and muscle pain. Strength and function did not change, and the authors noted that the study's size and duration were insufficient to evaluate functional end points.

In a placebo-controlled phase IIb trial in 123 older adults recovering from hip fracture, IGF-1 rose and gait speed improved, but the difference from placebo in stair-climbing power was not significant and several other functional measures did not improve. The trial was stopped early because of a safety signal of congestive heart failure in a limited number of patients, and the authors concluded that MK-0677 had an unfavourable safety profile in that population (Adunsky et al., 2011). MK-677 (ibutamoren): what the research says covers further studies.

What a buyer can verify about an MK-777 batch

With no literature, the batch certificate of analysis is the only independent document about what is in the bottle. Every Free Muscle-brand batch, MK-777 included, is assayed by Janoshik Analytical, an independent laboratory, and the certificate for a batch is sent by email on request, quoting the batch number. Our guide to reading a certificate of analysis covers the general layout.

Identity by LC-MS needs something to compare against

Liquid chromatography with mass spectrometry (LC-MS) separates a sample into components and measures their masses, but a mass confirms identity only when compared with something. For MK-677 anyone can make that comparison: calculated from PubChem's formula, ibutamoren's protonated molecule falls near m/z 529. MK-777 has no published structure, so the identity line on its certificate is the only statement of what the molecule is. Check that it names a specific compound or gives a formula: a named compound can be checked against PubChem, while a result reading only "MK-777" cannot.

What a missing reference standard means

Anti-doping laboratories confirm identity by comparing the retention time and diagnostic ion abundances of a sample with those of a reference specimen of the substance analysed in the same batch, within set tolerances (WADA TD2023IDCR). Those rules bind doping-control laboratories, not commercial certificates, but they show what confirmed identity involves. Without reference material, a mass that fits a proposed formula is weaker evidence, because different molecules, isomers included, can share a formula. Without literature, even a confirmed identity says nothing about what a molecule does.

Purity, content, batch and date

  • Purity by HPLC is the share of detected material that is one component: how clean the sample is, not what that component is.
  • Content is the measured amount per capsule against the label claim, where tested.
  • Batch number and test date must match the bottle. A certificate for another batch, or a generic PDF with no batch number, says nothing about that bottle.

Labels alone are not evidence. Of 44 products sold online as SARMs and analysed by US researchers, only 23 contained a SARM; a further 17 contained another unapproved drug, ibutamoren among them; no active compound was detected in four; 11 contained substances not on the label; and in only 18 did the amount of active compound match the label (Van Wagoner et al., 2017). Our lab tests page covers batch testing, and the UK supplier checklist sets out what else to check.

Is MK-777 legal in the UK?

MK-777 is not a licensed medicine. Under regulation 2 of the Human Medicines Regulations 2012, a medicinal product is any substance presented as having properties of preventing or treating disease in human beings, or that may be used by or administered to human beings with a view to restoring, correcting or modifying a physiological function by exerting a pharmacological, immunological or metabolic action, or making a medical diagnosis. Under regulation 46, a person may not sell or supply, or offer to sell or supply, an unauthorised medicinal product, meaning one without a UK marketing authorisation, certificate of registration, traditional herbal registration or Article 126a authorisation. MK-777 holds none of these.

The MHRA decides whether a product falls within that definition, looking at the claims made for it, the properties of its ingredients, its primary intended purpose or how consumers would use it, and how it is presented, including online (MHRA, 2026). A "research use only" label does not by itself decide the question. MK-777 is not sold as a medicine, food or food supplement and is not for human consumption; Free Muscle supplies it for laboratory research only, to adults aged 18 or over.

MK-777, Acetamoren and ibutamoren are not named in Schedule 2 of the Misuse of Drugs Act 1971, the list of controlled drugs, and legislation.gov.uk showed no outstanding amendments when we checked. Schedule 2 also defines some groups of controlled substances by chemical structure, so a name check is not conclusive for a molecule whose structure is unpublished. Our page on MK-677 legal status in the UK covers MK-677.

MK-777 and WADA: why an unlisted name can still be prohibited

Neither name appears on the 2026 WADA Prohibited List, but the list catches substances by description as well as by name, and two sections are relevant (WADA Prohibited List 2026).

  • S2.2.4, growth hormone releasing factors. This covers growth hormone secretagogues and their mimetics, naming ibutamoren (MK-677), anamorelin, ipamorelin, macimorelin and others, and S2 extends to other substances with similar chemical structure or similar biological effect. Everything in S2 is prohibited at all times and is a non-Specified Substance.
  • S0, non-approved substances. Any pharmacological substance not addressed by a later section of the list and with no current approval by any governmental regulatory health authority for human therapeutic use, designer drugs included, is prohibited at all times.

Which section, if any, applies depends on what the molecule is and does, which for MK-777 is unpublished. The conservative position for anyone subject to anti-doping rules is to treat it as prohibited at all times. No excretion or detection study has been published under either name, so no detection window is established. The list is revised yearly, each edition taking effect on 1 January.

Common questions

Is MK-777 just MK-677 under another name?

No published study or database record links the two. MK-677 is ibutamoren, a defined molecule with a CAS number and randomised human trials. MK-777 is a product designation with no published structure, so the name cannot show whether, or how, its contents relate to ibutamoren. The identity line on the batch certificate states what a batch contains.

What does MK-777 do?

No published study has measured what MK-777 does, in cells, animals or people, so this article describes no effect and makes no claim about results. Descriptions of its action found online cannot be traced to published data, and the MK-677 findings above describe a different compound. What a batch contains, as distinct from what it does, is a question for its certificate of analysis.

Is MK-777 a SARM or a peptide?

Neither label can be confirmed, because no structure or receptor data have been published under the name. A SARM is defined by action at the androgen receptor and a peptide by a chain of amino acids: both are questions about the molecule, not the name. Free Muscle files MK-777 beside MK-677, not in its SARMs or peptides ranges.

What side effects does MK-777 have?

They are unknown. No study of MK-777 has been published, so no adverse effects have been measured or reported under either name. That is an absence of data, not evidence of tolerability. For context only, MK-677 trials recorded increased appetite, lower-limb swelling, muscle pain, higher fasting glucose, lower insulin sensitivity and raised cortisol, and one trial was stopped early over a congestive heart failure safety signal. None of that can be assumed, in either direction, for MK-777.

Are there Acetamoren studies, reviews or Reddit reports?

No studies have been published under either name, as the search table above shows, and the PubMed records for the similar code MK-0777 concern a different molecule. Forum posts and reviews cannot establish what a product contained, because the contents were not analysed. For evidence about a batch, ask us by email for its certificate of analysis, quoting the batch number.

What about MK-777 dosage, benefits and results?

We do not publish dosing, timing, cycle or combination information for MK-777 or any research compound, and we make no claims about benefits, results or before-and-after outcomes. For MK-777 there are no measured results of any kind to report. It is sold for laboratory research only, to adults aged 18 or over.

Related reading

MK-777 (Acetamoren) and MK-677 are sold by Free Muscle for laboratory research use only. They are not licensed medicines, have not been evaluated by the MHRA, EMA or FDA, are not food supplements and are not for human consumption. Customers must be 18 or over. MK-677 is prohibited in sport under section S2 of the WADA Prohibited List, and MK-777 should be treated as prohibited. No pharmacological, effect or safety claim is made for MK-777, nothing on this page is medical, dosing or usage advice, and the studies summarised describe other compounds.

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):7001-7005. PMID: 7624358.
  2. 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):601-611. PMID: 18981485.
  3. Adunsky A, Chandler J, Heyden N, 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;53(2):183-189. PMID: 21067829.
  4. Van Wagoner RM, Eichner A, Bhasin S, Deuster PA, Eichner D. Chemical Composition and Labeling of Substances Marketed as Selective Androgen Receptor Modulators and Sold via the Internet. JAMA. 2017;318(20):2004-2010. PMID: 29183075.
  5. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026, sections S0 and S2.2.4. In effect from 1 January 2026. wada-ama.org.
  6. World Anti-Doping Agency. Technical Document TD2023IDCR: Minimum criteria for chromatographic-mass spectrometric confirmation of the identity of analytes for doping control purposes. Version 1.1, 14 February 2023. wada-ama.org.
  7. The Human Medicines Regulations 2012 (SI 2012/1916), regulations 2 and 46. legislation.gov.uk.
  8. Medicines and Healthcare products Regulatory Agency. Borderline products: how to tell if your product is a medicine. GOV.UK guidance, last updated 2 July 2026.
  9. Misuse of Drugs Act 1971, Schedule 2 (controlled drugs). legislation.gov.uk.