MK-677 & TB-500 Capsule Bundle

The Yakka Strength MK-677 and TB-500 capsule bundle lists ibutamoren (MK-677), a growth hormone secretagogue, together with TB-500, a synthetic fragment of thymosin beta-4, from one manufacturer in a single order through our Muscle Market range. Yakka Strength lists the pack as 60 capsules. No content per capsule is stated by the manufacturer on this listing, so we do not quote one. Supplied to adults for laboratory research only and not for human consumption.

A bundle is a listing convenience only: it lets separately packaged products from one manufacturer be ordered in a single purchase. Nothing on this page claims that they act together or should be studied together, and Free Muscle publishes no stack or cycle guidance for any product.

About the compounds in this bundle

MK-677 (Ibutamoren)

Ibutamoren (MK-677, L-163,191, nutrobal) is not a SARM but an orally active ghrelin receptor (GHS-R1a) agonist, a growth hormone secretagogue. Unusually for this market it has real human data. A one-year randomised trial in healthy older adults reported sustained rises in growth hormone and IGF-1, a 1.1 kg rise in fat-free mass against a 0.5 kg fall with placebo, but no change in strength or function, alongside increased appetite, mild leg swelling from fluid retention, muscle pain, higher fasting glucose, reduced insulin sensitivity and a rise in cortisol. Never approved. WADA class S2. Compare brands on the MK-677 (Ibutamoren) collection page.

A later phase IIb trial tested the compound, under the code MK-0677, in 123 older patients recovering from hip fracture. Blood IGF-1 rose clearly against placebo and gait speed improved modestly, but most other measures of physical function did not change, and the study was stopped early after a small number of patients developed congestive heart failure. The authors concluded that the compound had an unfavourable safety profile in that population.

TB-500 (Thymosin Beta-4 fragment)

TB-500 is the market name for a synthetic fragment of thymosin beta-4, a 43-amino-acid actin-binding peptide made in the body. Reviews of thymosin beta-4 cover preclinical wound, corneal and cardiac repair models and early clinical trials of the full peptide. TB-500 itself has no published human data. WADA names thymosin beta-4 and its derivatives, including TB-500, under S2. Compare brands on the TB-500 (Thymosin Beta-4 fragment) collection page.

What TB-500 actually contains was settled analytically rather than clinically. In 2012 the Ghent anti-doping laboratory examined a product sold as TB-500 by high-resolution mass spectrometry and found the acetylated 17-23 fragment of thymosin beta-4, Ac-LKKTETQ, a seven-residue peptide, instead of the whole protein. So a TB-500 label and the thymosin beta-4 literature need not describe the same molecule.

At a glance

This listing

• Brand: Yakka Strength (third-party brand, Muscle Market)
• Compounds: ibutamoren (MK-677) and TB-500 (thymosin beta-4 fragment)
• Form and pack size: 60 capsules, as listed by the manufacturer
• Content per capsule: not stated by the manufacturer
• Which TB-500 molecule: not stated on the label
• COA: only where Yakka Strength supplies one for the batch held

Because neither compound carries a stated content, milligrams per pack cannot be worked out and the bundle cannot be compared with single packs on cost per milligram; our price per milligram guide sets out the method for products that do state a strength. The same manufacturer's MK-677 capsules and TB-500 capsules are also listed on their own.

MK-677 and TB-500 in the UK: buying, legal status and what to check

Searches such as "MK677 UK buy" and "MK 677 UK legal" ask two things: is the purchase lawful, and can the seller show what is in the container.

Where the law stands

None of the compounds on this page is a licensed medicine in the United Kingdom, none has been assessed by the MHRA and none is an authorised food supplement. MK-677 and TB-500 are not controlled substances in the UK, but that is not approval: neither may lawfully be marketed for people to take. Free Muscle supplies them to adults aged 18 and over for laboratory research only. They are not for human consumption. Both MK-677 and TB-500 fall under WADA class S2. See our MK-677 legal status page. Our SARMs research guide has more background.

Signs of a listing worth trusting

• A stated strength for each compound, or an open statement that the manufacturer gives none.
• The exact molecule named: for TB-500 that means saying whether it is the Ac-LKKTETQ fragment or full thymosin beta-4.
• A lot number printed on each container and repeated on the certificate that goes with it.
• A certificate per compound per batch, from a named laboratory, not a single report headed with the bundle name.
• Research-only wording: 18+, no instructions, no promised outcomes, no before-and-after images.
• A UK company you can write to, tracked delivery, plain packaging and a published returns policy.

How this listing measures up

The seller side is met. FreeMuscle LTD is a UK company based in Scunthorpe; every order ships 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 product side depends on Yakka Strength. The label names both compounds but states no content for either and does not say which TB-500 molecule is used, so those checks are not met from the label alone. A certificate is shown only where the manufacturer supplies one for the batch we hold. The full set of checks is in our UK supplier checklist.

Capsules compared with other forms

In the UK research market ibutamoren is found as capsules, tablets and liquid ("MK677 UK liquid" is a frequent search), while TB-500 is most often sold as freeze-dried powder in vials, with capsules a more recent format. The molecule is the same; the evidence behind each route is not.

Ibutamoren. Merck designed it as a non-peptide precisely so that it would remain active when swallowed, and both trials summarised above gave it by mouth. A capsule is therefore the route its literature actually studied. In a liquid, hydrolysis, evaporation and incomplete dissolution can shift the concentration; a capsule fixes its fill at manufacture, so its consistency rests on how evenly the powder was blended.

TB-500. Here the capsule is the unusual choice. The thymosin beta-4 programmes used injection or direct application to eye, skin or heart tissue, and no published study has given either the full protein or the Ac-LKKTETQ fragment by mouth and measured it in blood. Peptides face digestive enzymes that cut the bonds between amino acids. Our article Do oral peptides actually work? sets out what is and is not known about oral peptide absorption. None of this implies that any format produces an effect.

TB-500 compared with BPC-157, and MK-677 with ipamorelin

Each compound in this bundle has one relative it is searched against far more than any other: "TB 500 vs BPC 157" and "ibutamoren vs ipamorelin".

TB-500 and BPC-157

The two peptides are often shelved together, but they share neither origin nor mechanism. TB-500 traces back to thymosin beta-4, a protein that sits inside cells and holds single actin units in reserve. BPC-157 is a 15-amino-acid sequence taken from a protein found in gastric juice, and nearly all of its published work comes from rodent gut, tendon and blood vessel models. Neither peptide has a published controlled human trial. The clearest practical difference is definition: BPC-157 is one fixed sequence, so identity testing is simple, whereas "TB-500" has been applied to more than one molecule, so a certificate has to say which it found. The two also sit in different parts of the WADA list, TB-500 under S2 and BPC-157 under S0 for non-approved substances. Brands we hold are in the BPC-157 collection.

MK-677 and ipamorelin

Here the comparison is closer, because both act at the same ghrelin receptor and prompt the pituitary to release growth hormone it already stores. The differences are structure and evidence. Ibutamoren is a small molecule tested by mouth in randomised human trials, with the adverse findings described above. Ipamorelin is a five-residue peptide developed by Novo Nordisk in the 1990s, studied mostly by injection and with a far thinner human literature. Neither is licensed in the UK and WADA lists both under S2. Brands are in the ipamorelin collection, and the MK-677 vs ipamorelin vs somatropin article covers the question in depth.

Reading the certificate of analysis for this product

Yakka Strength is a third-party brand sold through Muscle Market. For third-party brands we display a certificate of analysis only where the manufacturer supplies one for the exact batch we hold; if none is shown, none has been supplied and we do not substitute a generic document. Free Muscle-brand products, by contrast, are assayed batch by batch at Janoshik Analytical, with the certificate sent on request by email. Our lab testing page explains what a certificate shows.

Expect two reports, one per compound, and read each against its own container.

1. Identity. HPLC compares a peak with a reference standard; LC-MS also measures the mass, which is the firmer evidence. Ibutamoren, at 528.7 g/mol, should appear as a protonated ion close to m/z 529. For TB-500 the mass tells you which molecule is present: the Ac-LKKTETQ fragment weighs roughly 889 g/mol, while full thymosin beta-4 is near 4,963 g/mol and shows as a cluster of multiply charged ions.
2. Purity (%). The main compound's share of the chromatogram. It measures how clean the material is, not how much is in each capsule.
3. Assay. Milligrams found per capsule, the one figure that would replace the missing label strength; peptide results may be given as net peptide or as gross powder weight.
4. Batch number. It has to match the lot printed on that container; a different number means the report describes other stock.
5. Test date and laboratory. The test date should fall after the batch was made, and the laboratory should be named so the report can be checked with it.

For this brand, a missing identity line leaves the TB-500 question open, a missing content line leaves both strengths unknown, and a report headed only "MK-677 and TB-500 bundle" cannot show which compound was tested. Contact us with the lot numbers and we will say what exists for current stock. See also how to read a certificate of analysis.

Detection, sport and testing

Both compounds are prohibited at all times, in and out of competition, under the World Anti-Doping Code, which UK Anti-Doping applies in this country. Ibutamoren is named in section S2 among the growth hormone secretagogues; TB-500 falls under the same section through the entry for thymosin beta-4 and its derivatives. Under strict liability a competitor is answerable for anything found in their sample. A research-use label or a certificate of analysis offers no defence in an anti-doping case.

Anti-doping laboratories have worked on TB-500 for over a decade. The 2012 Ghent study that identified the Ac-LKKTETQ fragment also proposed an LC-MS/MS strategy for finding it in plasma and urine. No study cited on this page reports how long either ibutamoren or TB-500 remains detectable in human urine after exposure, so the accurate statement for both is: detectable, window not established. Anyone who is subject to testing should assume that contact with either compound will be found.

Storage, stability and handling

No published stability study covers either compound in capsule form, so the expiry or best-before date printed by the manufacturer, where one is given, is the limit to work within. The two compounds are vulnerable in different ways. For ibutamoren the main risks come from the capsule itself: humidity softens gelatin and clumps powder. TB-500 is a peptide, so water is the bigger concern, since it breaks peptide bonds over time; the full thymosin beta-4 protein also carries a methionine that oxidises easily, a reaction light can accelerate.

In practice: keep the containers sealed in a cool, dry, dark cupboard, away from bathrooms and radiators. Leave any desiccant sachet in place. If stock is kept in a fridge, allow the container to reach room temperature before opening so moisture does not condense on the capsules. Store each compound in its own labelled container so that it stays tied to its lot number and certificate. Treat the contents as laboratory reagents: wear gloves when handling opened capsules, keep them apart from food and drink and out of reach of children and pets, and dispose of unwanted material as chemical waste rather than in household bins or drains.

Glossary

• Ibutamoren: the international name for MK-677, also coded L-163,191 and MK-0677.
• Ghrelin receptor (GHS-R1a): the receptor on pituitary cells that ibutamoren and ipamorelin activate.
• IGF-1: insulin-like growth factor 1, whose blood level rose in both ibutamoren trials.
• Phase IIb trial: a mid-stage study of a candidate medicine in patients with the target condition.
• Thymosin beta-4: a 43-amino-acid protein present in most cells; TB-500 products are based on it.
• Ac-LKKTETQ: the acetylated seven-residue fragment (positions 17 to 23) of thymosin beta-4 found in TB-500 by anti-doping analysts.
• G-actin: single, unpolymerised units of actin, the protein that builds a cell's internal scaffolding.
• Mass spectrometry: weighing ionised molecules, reported as m/z, to confirm what a sample is.
• Net peptide content: the share of a peptide powder that is the peptide itself, excluding water and counter-ions.
• WADA S2: the Prohibited List section for peptide hormones, growth factors, related substances and mimetics.

Related

• MK-677 (Ibutamoren) collection
• TB-500 (Thymosin Beta-4) collection
• Yakka Strength brand page
• Peptides collection
• Bundles collection
• Research articles: MK-677: what the research says and TB-500 and thymosin beta-4 research guide
• Delivery and returns

Supplied for laboratory research use only. Not a medicine, not evaluated by the MHRA, EMA or FDA, and not for human consumption. Buyers must be 18 or over. Nothing on this page is medical or dosing advice or a recommendation to use, stack or cycle any compound; research summaries describe findings in study participants or animals, not claims about this product.

References

1. 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.
2. 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.
3. Goldstein AL, et al. Thymosin beta4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert Opin Biol Ther. 2012;12(1):37-51. PMID: 22074294.
4. Esposito S, et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential. Drug Test Anal. 2012;4(9):733-8. PMID: 22962027.