MK-677

Yakka Strength MK-677 is a pack of 60 capsules of ibutamoren, the orally active growth hormone secretagogue better known by its development code MK-677. Yakka Strength manufactures it, and Free Muscle stocks it in the Muscle Market range for laboratory research by adults aged 18 and over. No per-capsule strength is given in the product information we hold for this listing, so none is quoted here.

About MK-677

Ibutamoren is also sold as MK-677, MK-0677, L-163,191, ibutamoren mesylate (its salt form) and Nutrobal. Merck designed it in the 1990s as a non-peptide molecule that reproduces the action of the growth hormone releasing peptides while remaining active when swallowed. It is not a SARM and does not target the androgen receptor. It activates the ghrelin receptor, GHS-R1a, which signals the pituitary to release growth hormone in pulses; the liver answers with more insulin-like growth factor 1 (IGF-1).

Identifier	Ibutamoren (free base)
CAS number	159634-47-6
Molecular formula	C27H36N4O5S
Molecular weight	528.7 g/mol
InChIKey	UMUPQWIGCOZEOY-JOCHJYFZSA-N
PubChem CID	178024

These PubChem values describe the free base. The 2011 trial below used ibutamoren mesylate, a salt, and that distinction matters on a certificate.

What the published research reports

Unusually for a research compound, ibutamoren has a real human trial record. In a 1996 placebo-controlled study, 32 healthy volunteers aged 64 to 81 were assigned to placebo or once-daily oral ibutamoren for two and four weeks. Growth hormone rose because existing pulses grew larger, not more frequent, and at the highest of the three daily amounts tested, IGF-1 reached the range typical of young adults. Fasting glucose and prolactin also rose.

The longest trial, published in 2008, randomised 65 healthy adults aged 60 to 81. Over the first year, fat-free mass rose by 1.1 kg with ibutamoren and fell by 0.5 kg with placebo, but strength and function did not change, total fat mass and abdominal visceral fat did not differ, and body weight and limb fat rose more than with placebo. Adverse findings included increased appetite, mild transient swelling of the lower legs, muscle pain, a 0.3 mmol/L rise in fasting glucose, reduced insulin sensitivity and higher cortisol. The authors judged the study too small and short to assess function.

Ibutamoren mesylate was also tested in a 2011 phase IIb trial in 123 older people recovering from hip fracture. IGF-1 went up and gait speed improved, while stair-climbing power and several other functional measures did not. Congestive heart failure in a small number of patients led to the trial being halted early, and the investigators concluded that the adverse-effect profile was unfavourable in that group. Merck did not take ibutamoren to approval. These findings describe study participants and are not claims about this product.

This listing

• Compound: MK-677 (Ibutamoren)
• Brand and manufacturer: Yakka Strength
• Form: capsules
• Pack size: 60 capsules
• Strength per capsule: not stated in the product information we hold
• Total per pack: cannot be calculated without a stated strength
• Intended use: laboratory research only, not for human consumption
• Sold to adults aged 18 and over

With no stated strength, neither milligrams per pack nor cost per milligram can be worked out, so this pack cannot be ranked against brands that print a figure (method: price per milligram). Only a batch certificate can supply a measured content.

MK-677 in the UK: buying, legal status and what to check

Three of the commonest UK searches, "MK 677 UK legal", "MK677 UK buy" and "MK677 UK supplier", raise two questions: may it be bought here, and what separates a sound seller from a poor one.

The legal position

UK law does not list ibutamoren as a controlled drug, but being uncontrolled is not the same as being approved. Without an MHRA marketing authorisation it cannot be marketed as a medicine, and as it is neither an authorised food supplement nor an authorised novel food, it cannot be marketed as food. It cannot lawfully be sold for human consumption. That leaves supply as a research compound for laboratory work: the only way Free Muscle lists it, and only to buyers aged 18 or over. In sport it is banned at all times (see detection, below), and buyers are responsible for the rules that apply to them, including any anti-doping code. Detail is on our MK-677 legal status in the UK page.

What a trustworthy UK listing shows

• A lot number printed on the pack, which is what links the contents to any test result.
• A batch-specific certificate of analysis, rather than a generic or undated PDF.
• A stated strength per capsule, ideally saying whether it means free base or mesylate salt.
• A manufacturer's name, plus a UK seller with a registered company and a way to reach it.
• Research-use terms: 18+ only, no usage directions, no promised outcomes.
• Tracked delivery in plain packaging and a published returns policy.

How this listing measures up

Measured against that list, the seller, research-use and delivery points are met outright. FreeMuscle LTD is a UK company in Scunthorpe, the manufacturer is named, and every order goes by free tracked UK delivery in plain packaging. Orders placed before 2pm Monday to Friday are processed the same working day, EU delivery takes 3-7 working days, and unopened items can be returned within 30 days. The certificate point depends on the batch, because a Yakka Strength COA is shown only where the manufacturer supplies one. The strength point is not met: the product information we hold gives no figure. Price searches meet the same limit: prices change and appear on the listing itself, and a fair comparison is price per milligram, which needs a stated strength. More checks are in our UK supplier checklist.

Capsules compared with other forms

Searches for "MK 677 tablet", "MK677 tablets" and "MK677 UK liquid" show that ibutamoren turns up in several formats: capsules, pressed tablets and so-called research liquids. The active molecule does not change between them; the way each unit's content is fixed, and how well that content holds up, does.

• Capsules contain a set fill of powder, normally mixed with a bulking excipient. How evenly that blend was mixed decides how consistent each capsule is, and the shell keeps the dry powder largely away from air and moisture.
• Tablets add compression and binders to the same blending step, so their content is likewise fixed when they are made.
• Liquids depend on complete and lasting dissolution, and each drawn volume is only as accurate as the pipette used. In solution most compounds degrade faster than when dry, and if solvent evaporates the concentration creeps upward.

Because ibutamoren is a small non-peptide molecule, the enzymatic digestion that limits peptides taken by mouth does not apply to it in the same way; it was designed to be orally active, and the 1996 and 2008 trials above gave it by mouth. Peptide secretagogues are in the opposite position (see do oral peptides work). None of this suggests any format produces an effect. The practical difference is verification: a capsule certificate can report content per capsule, a liquid one reports concentration.

MK-677 compared with ipamorelin

Of the related compounds, ipamorelin is the one most often searched against this one ("ibutamoren vs ipamorelin"). The two share a receptor, GHS-R1a, and a mode of action: each makes the pituitary release growth hormone it already holds. Almost everything else that can be documented about them differs.

Point	MK-677 (ibutamoren)	Ipamorelin
Chemical type	Non-peptide small molecule	Synthetic pentapeptide
Formula	C27H36N4O5S	C38H49N9O5
Molecular weight	528.7 g/mol	711.9 g/mol
Origin	Merck, 1990s	Novo Nordisk, described 1998
Human trials	Several randomised trials, up to two years	Few, none measuring muscle or strength that we know of
UK status	Unlicensed research compound	Unlicensed research compound
WADA	S2.2.4, named	S2.2.4, named

First, route: ibutamoren was built to survive the gut, whereas ipamorelin is a chain of five amino acids of the kind digestive enzymes break down, so oral ipamorelin products have no published clinical evidence behind them that we know of. Second, evidence: ibutamoren's trials measured body composition and recorded adverse effects, from raised glucose to the heart failure signal after hip fracture, while ipamorelin's human literature is thin. Third, status, where they converge: neither is licensed in the UK or a controlled drug, and WADA names both in section S2.2.4 as growth hormone secretagogues, prohibited at all times.

A PubMed search for both names together returns reviews, chemistry and animal work but no head-to-head trial in people, so neither can be called stronger, and we do not rank research compounds by effect. Brands held are in the ipamorelin collection, both are set against prescription somatropin in MK-677 vs ipamorelin vs somatropin, and the peptide's own studies are summarised in the ipamorelin research guide.

Reading the certificate of analysis for this product

Yakka Strength manufactures this product, so a certificate of analysis (COA) for it can only come from them. We display one only when they have provided it for the batch in our stock, either linked here or emailed on request; where there is none, we state that plainly instead of posting a generic PDF. Free Muscle's own MK-677 capsules (10mg, 12.5mg and 25mg) are assayed batch by batch at Janoshik Analytical, an independent laboratory; that does not extend to Yakka Strength. On a Yakka Strength certificate, read:

• Identity (HPLC or LC-MS). HPLC infers identity from a peak matching a reference standard's retention time. LC-MS measures mass: ibutamoren gives a protonated ion near m/z 529, whether the sample was free base or mesylate, because the salt partner separates in solution.
• Purity (%). An HPLC peak-area share. It grades the material, not the capsule, and gives no milligram figure.
• Content per capsule, and in which form. The line this product needs most. Methanesulfonic acid adds about 96 g/mol, so free base is roughly 85 per cent of the mesylate salt by mass (528.7 divided by about 624.8); the two figures are not interchangeable.
• Batch number. Must match the lot on the pack in hand.
• Test date and laboratory. Shows the result's age and who can confirm it.

Gaps have plain consequences here. Without identity, nothing confirms the capsules hold ibutamoren; purity with no content line leaves the amount per capsule unknown; a missing or different batch number means the report belongs to another batch. Contact us with the lot number and we will confirm what exists for current stock. See also how to read a COA and our lab tests page.

Detection, sport and testing

WADA bans ibutamoren at all times, in and out of competition. Section S2.2.4 (growth hormone releasing factors) names "ibutamoren (MK-677)" as an example of a growth hormone secretagogue, and every substance in section S2 is non-Specified. Because it is named on the list, WADA-accredited laboratories test for it, and strict liability applies: an athlete answers for any prohibited substance in their sample, whatever its source.

For urine, the usual sample, a PubMed search found metabolism studies in horses but no published human excretion study, so the accurate statement is: detectable, window not established. Hair has some human data. In a forensic study from Strasbourg, ibutamoren was measured at 1.3 pg/mg in a male volunteer's hair collected four weeks after a single exposure (detection limit 0.1 pg/mg), and at 224 pg/mg in hair from a person who had taken it repeatedly for sporting purposes. Anyone subject to testing should assume exposure will be found.

Storage, stability and handling

Keep the pack closed in its original container somewhere cool, dry and dark, away from radiators, sunny windows and kitchen steam. Humidity is the main threat: shells absorb water and soften or fuse, and damp powder breaks down faster, while hot, very dry air makes shells brittle. If the pack is refrigerated, let it reach room temperature before opening so condensation does not form inside, and leave any desiccant sachet in the tub.

Shelf-life data for ibutamoren capsules do not appear in any published literature we could find, so the printed expiry or best-before date, where there is one, sets the limit. Record when the pack was first opened alongside its batch number. Handle it as a laboratory reagent: gloves for opened capsules or loose powder, away from food and drink, out of reach of children and animals, any removed portion labelled with compound, batch and date, and waste disposed of as chemical waste, not in household bins or drains. Never decant capsules into an unlabelled container; the batch number on the original pack is the only link to a certificate.

Glossary

• Growth hormone secretagogue: the drug class ibutamoren belongs to, defined by causing the pituitary to secrete more of its own growth hormone.
• GHS-R1a: the receptor through which the stomach hormone ghrelin acts; ibutamoren and ipamorelin both activate it.
• IGF-1: insulin-like growth factor 1, a hormone whose blood level tracks growth hormone output, most of it produced by the liver.
• Pulsatile secretion: the pattern in which growth hormone leaves the pituitary as a series of peaks, not a constant flow.
• Ibutamoren mesylate: the methanesulfonic acid salt of ibutamoren, heavier than the free base.
• Free base: the molecule without a salt partner.
• Fat-free mass: body mass minus fat, including water, so it rises with fluid retention as well as tissue.
• Oedema: swelling from fluid collecting in tissues.
• Insulin sensitivity: the degree to which muscle, liver and fat respond to insulin; lower sensitivity means glucose is cleared from the blood less readily.
• LC-MS: a liquid chromatograph feeding a mass spectrometer, so each separated component is also weighed as ions; the firmer identity test.
• m/z: mass-to-charge ratio, the value a mass spectrometer reports.
• Certificate of analysis (COA): one batch's laboratory results (identity, purity and content where measured), dated and carrying that batch's number.

Related

• MK-677 (Ibutamoren) collection: all brands held, with strength, pack size and testing set out for each
• All Yakka Strength products at Free Muscle
• MK-677 (ibutamoren): what the research says
• Delivery and returns

Not for human consumption. This Yakka Strength pack is supplied for laboratory research use only; it is neither a licensed medicine nor a food supplement, and neither the MHRA nor the EMA or FDA has evaluated it. Orders are restricted to adults aged 18 and over, and nothing on this page amounts to medical, dosing or usage advice.

References

1. Chapman IM, 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. PMID: 8954023.
2. 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;149(9):601-11. PMID: 18981485.
3. 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;53(2):183-9. PMID: 21067829.
4. Kintz P, Gheddar L. Knowing the minimal detectable dose can facilitate the interpretation of a hair test result: II. Case example with ibutamoren (MK-677), a growth hormone secretagogue. Clin Chim Acta. 2026;578:120578. PMID: 40882886.