YK-11 Capsules UK
3 products from 2 brands · free UK delivery · EU 3–7 days
Every YK-11 listing compared
Last reviewed · prices and listings checked by Free Muscle
Strength and pack size as stated by each manufacturer. Total milligrams = strength per capsule multiplied by capsules per pack. Price per milligram is calculated from the current price. A dash means the manufacturer does not state that figure.
| Brand | Listing | Strength | Pack | Total | Price | £ per capsule | Per mg | Availability |
|---|---|---|---|---|---|---|---|---|
| iMuscle | YK-11 — 60 caps, 10mg | 10mg | 60 capsules | 600mg | £42.99 | £0.72 | £0.072 | In stock |
| FreeMuscle | Research Bundle — MK-677 + RAD-140 + YK-11 | – | – | – | £100.00 | – | In stock | |
| FreeMuscle | YK-11 — Myostatin Inhibitor · 10mg · 60 Capsules | 10mg | 60 capsules | 600mg | £49.99 | £0.83 | £0.083 | In stock |
YK-11, also written YK11 and sold under names such as Myostine, is a synthetic steroid (CAS 1370003-76-1) first described by researchers at Toho University in Japan in 2011 as a partial agonist of the androgen receptor. It is often sold as a SARM and described as a myostatin inhibitor. This page lists every brand of YK-11 stocked at Free Muscle, compared on strength per capsule, capsules per pack and batch testing, and summarises what the published research does and does not show.
What is YK-11?
Unlike RAD-140, LGD-4033 or ostarine, YK-11 is built on a steroid skeleton: it is a 19-norpregnane derivative related to nandrolone, carrying an unusual orthoester group on its D-ring. In reporter-gene assays it activated the androgen receptor (AR) only partially, accelerated AR movement into the nucleus, and did so without inducing the amino/carboxyl-terminal (N/C) interaction that full agonists such as dihydrotestosterone rely on. Because it produced gene-selective effects, the Toho group suggested it might function as a SARM despite its steroidal structure.
The myostatin claim began with a cell-culture finding. In mouse C2C12 myoblasts, YK-11 induced expression of follistatin, an endogenous antagonist of myostatin, and the myogenic differentiation it caused was reversed by an anti-follistatin antibody (2013). A 2021 study in septic mice also described YK-11 as a myostatin inhibitor, but no study in people has tested the idea, so for humans it remains a hypothesis. YK-11 has no pharmaceutical developer, was never entered into clinical trials, and has never been approved as a medicine by the MHRA, EMA, FDA or any other regulator. Anti-doping scientists have characterised it from a seized black-market product.
Identity, as recorded in PubChem:
- CAS number: 1370003-76-1
- Molecular formula: C25H34O6
- Molecular weight: 430.5
- PubChem CID: 119058028
- Chemical name: (17alpha,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester
What the published research reports
The evidence is preclinical: cell studies, rodent studies and doping-control chemistry. Nobody has published a human trial of YK-11, and none was registered on ClinicalTrials.gov when we checked on 2 October 2026.
| Study | Model | What was reported | Limits |
|---|---|---|---|
| Kanno 2011 | Androgen-response-element luciferase assay; MDA-MB 453 cells | Partial agonist of the AR that accelerated its nuclear translocation without inducing the N/C interaction, and blocked DHT from inducing it; effects on gene expression varied by gene | Cells only |
| Kanno 2013 | C2C12 mouse myoblasts | Stronger induction of MyoD, Myf5 and myogenin than DHT; induced follistatin, and an anti-follistatin antibody reversed the differentiation | Cells only; the source of the myostatin label |
| Yatsu 2018 | MC3T3-E1 mouse osteoblasts | Faster proliferation and mineralisation, more osteoprotegerin and osteocalcin and raised phosphorylated Akt, all attenuated by an AR antagonist | Cells only |
| Piper 2018 | YK-11 identified in a seized black-market product; elimination study with deuterium-labelled YK-11 | 14 metabolites found in urine, none of them intact YK-11; glucuronide and sulfate conjugates still detectable beyond 48 hours; two adopted for routine anabolic-agent screening | Designed for doping control, not to measure effects |
| Lee 2021 | Mice with gram-negative sepsis | Myostatin and follistatin rose in septic muscle; YK-11, described as a myostatin inhibitor, brought down inflammatory cytokines and markers of organ damage and cut deaths from sepsis | Mouse infection model only |
| Dahleh 2023 | Male Wistar rats, five weeks, with or without swimming exercise | More oxidative stress and poorer mitochondrial function in the hippocampus; swimming blocked part of the mitochondrial damage, but not the oxidative stress | Rats only |
| Dahleh 2024 | Rats, five weeks, with or without swimming exercise | Lower hippocampal BDNF/TrkB/CREB signalling, higher IL-1beta and IL-6, lower IL-10, raised p38 MAPK activity and activation of the Bax/Bcl-2/caspase-3 apoptotic cascade, with impaired aversive memory consolidation; exercise offset some changes | Rats only |
| Sobolevsky 2024 | Doping control sample | The UCLA Olympic Analytical Laboratory reported detecting YK-11 in a doping control sample | A detection report, not an effect study |
| Wang 2025 | Bone-marrow mesenchymal stem cells; rats with skull defects | Promoted bone-forming differentiation and, as a YK-11-loaded hydrogel, repair of skull defects; both effects were suppressed when the AR was inhibited | Local application in rats; the proposed BMP2/Smad pathway is not established in people |
These findings describe cell lines, laboratory animals and doping-control samples. None of them is a claim about the products listed on this page.
Brands of YK-11 we stock
- Free Muscle YK-11, 10mg, 60 capsules. Our own brand, capsule form, 600mg of compound per pack. Every batch is assayed by Janoshik Analytical and the certificate for your batch is available by email on request. View the Free Muscle YK-11 listing.
- iMuscle YK-11, 10mg, 60 capsules. Capsule form, 600mg per pack. A certificate of analysis is shown on the listing only where iMuscle has supplied one for the batch we hold. View the iMuscle YK-11 listing.
How to compare them
Both listings hold 600mg per pack (10mg multiplied by 60 capsules), and the comparison table above gives the price per milligram for each, so the real difference is testing. The Free Muscle batch has a Janoshik identity and purity assay for its lot number; for the iMuscle batch, it depends on whether the manufacturer has provided a certificate. Because YK-11 has turned up in seized black-market material analysed by doping scientists, independent confirmation of identity matters more here than for most compounds. Our guide to price per milligram covers the arithmetic.
Batch testing and certificates of analysis
YK-11 is harder to certify than most compounds sold as SARMs. Mass spectrometry can confirm a match with its formula, C25H34O6, and molecular weight, 430.5, and the PubChem InChIKey, KCQHQCDHFVGNMK-PQUNLUOYSA-N, encodes the full structure for comparison. A purity percentage on its own, however, does not show that the geometry at each stereocentre and at the E double bond is as described. The Cologne doping-control group also called the orthoester-derived group on its D-ring arguably labile, so unexpected extra peaks in a chromatogram may be breakdown products rather than random impurities.
Janoshik Analytical, an independent laboratory, assays every Free Muscle batch of YK-11, and its certificate is emailed on request with the batch number from the label. The iMuscle listing carries a certificate only when iMuscle has sent us one covering the batch in our stock. A document with no lot number or test date is not a batch certificate. Our lab tests page walks through matching a certificate to its batch.
Where to buy YK-11 in the UK: how to check a supplier
Whichever shop you buy YK-11 from, check these five points before you order:
- A batch number and a certificate for that batch. The pack should carry a batch number, and the seller should be able to show a certificate of analysis for that same batch from a named laboratory, with the test date. Every Free Muscle-brand batch is assayed by Janoshik Analytical, and we send the certificate for your batch on request. For iMuscle, a certificate is shown where the brand supplies one for the batch we hold.
- The strength per capsule and the capsule count. With both figures you can work out the total milligrams in the pack and the price per milligram; the comparison table above does this for every listing here that states both. If a listing does not state one of them, ask the seller before you order.
- Research-use labelling and an age check. A research compound should be sold for laboratory research use only, not for human consumption, to adults aged 18 or over, with no dosing or usage advice. That is how every listing here is sold.
- Prices in pounds sterling and tracked UK dispatch. UK delivery from us is free and tracked on every order, with no minimum spend, and usually arrives 2-3 working days after dispatch; orders placed before 2pm Monday to Friday are processed the same working day.
- A clear returns policy. Unopened items can be returned to us within 30 days.
Brands on this page: Free Muscle and iMuscle. The UK supplier checklist and how we test go into more detail.
Legal status in the UK
YK-11 is not named in the Misuse of Drugs Act 1971, although the Act also defines some anabolic steroids by chemical structure rather than by name. It has no MHRA marketing authorisation and cannot be sold as a medicine, and the Food Standards Agency, according to UK Anti-Doping, regards SARMs as unauthorised novel foods, which keeps them out of food and dietary supplements. Free Muscle sells YK-11 for laboratory research alone, to customers who are 18 or older.
YK-11 is one of the SARMs given as examples in S1.2, other anabolic agents, of the 2026 WADA Prohibited List, so it is banned in and out of competition, and UK Anti-Doping lists it as YK-11 (Myostine). For the wider class, see our research guide to SARMs.
Storage and handling
Orthoester groups as a class are split by water, particularly under acidic conditions, and the one in YK-11 has been described as arguably labile, so keep the capsules dry: sealed in the original, batch-numbered bottle in a cool, dark place, with any desiccant left in, away from children and pets, and handle it with ordinary laboratory good practice. Fuller notes on condensation, signs of degradation and disposal are on the Free Muscle YK-11 page.
Delivery and returns
All orders are sent from our UK operations in Scunthorpe, with free tracked UK delivery and plain packaging. Place an order before 2pm Monday to Friday and it is processed that working day; EU orders take 3 to 7 working days to arrive. Unopened items may be returned within 30 days. Customers must be 18 or over. Our shipping page and guarantee page have the full terms.
Related reading
- What are SARMs? The 2026 research guide
- SARMs explained: how selective androgen receptor modulators work
- How to read a certificate of analysis
- What is Janoshik Analytical?
- How to choose a SARMs supplier in the UK: a checklist
Related collections: RAD-140 (Testolone), MK-677 (Ibutamoren), LGD-4033 (Ligandrol), all SARMs.
References
- Kanno Y, et al. (17alpha,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester (YK11) is a partial agonist of the androgen receptor. Biol Pharm Bull. 2011;34(3):318-323. PMID: 21372378.
- Kanno Y, et al. Selective androgen receptor modulator, YK11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression. Biol Pharm Bull. 2013;36(9):1460-1465. PMID: 23995658.
- Yatsu T, et al. Selective Androgen Receptor Modulator, YK11, Up-Regulates Osteoblastic Proliferation and Differentiation in MC3T3-E1 Cells. Biol Pharm Bull. 2018;41(3):394-398. PMID: 29491216.
- Piper T, et al. Studies on the in vivo metabolism of the SARM YK11: Identification and characterization of metabolites potentially useful for doping controls. Drug Test Anal. 2018;10(11-12):1646-1656. PMID: 30379415.
- Lee SJ, et al. Myostatin inhibitor YK11 as a preventative health supplement for bacterial sepsis. Biochem Biophys Res Commun. 2021;543:1-7. PMID: 33588136.
- Dahleh MMM, et al. YK11 induces oxidative stress and mitochondrial dysfunction in hippocampus: The interplay between a selective androgen receptor modulator (SARM) and exercise. J Steroid Biochem Mol Biol. 2023;233:106364. PMID: 37468001.
- Dahleh MMM, et al. From gains to gaps? How Selective Androgen Receptor Modulator (SARM) YK11 impact hippocampal function: In silico, in vivo, and ex vivo perspectives. Chem Biol Interact. 2024;394:110971. PMID: 38521455.
- Sobolevsky T, et al. Detection of selective androgen receptor modulator YK-11 in a doping control sample. Drug Test Anal. 2024;16(6):655-660. PMID: 37946705.
- Wang R, et al. YK11 promotes osteogenic differentiation of BMSCs and repair of bone defects. J Mol Endocrinol. 2025;74(2):e240073. PMID: 39660819.
- UK Anti-Doping. SARMs (supplement ingredient warning). Last updated 29 April 2026.
Research compounds sold by Free Muscle are supplied for laboratory research use only and are not for human consumption. They are not authorised as medicines by the MHRA, EMA or FDA, are not food supplements, and are sold only to adults aged 18 or over. Nothing on this page is medical or dosing advice. Summaries of published research describe study findings and are not claims about any product.
Research guides
Frequently asked questions
Is YK-11 legal in the UK?
YK-11 does not appear by name in the Misuse of Drugs Act 1971, although the Act also defines some anabolic steroids by chemical structure. It is unlicensed: the MHRA has never granted it a marketing authorisation, and SARMs are unauthorised novel foods in the Food Standards Agency's view, so it cannot be sold or labelled for human consumption. Free Muscle supplies YK-11 for laboratory research only, to adults aged 18 or over.
Is YK-11 a SARM or a steroid?
Chemically YK-11 is a steroid: a 19-norpregnane derivative related to nandrolone with an orthoester group on its D-ring. It is called a SARM because it acted as a partial, gene-selective androgen receptor agonist in cell assays. Most compounds sold as SARMs are non-steroidal, so YK-11 is an outlier in the class, and WADA lists it as an anabolic agent.
Is Myostine the same as YK-11?
Myostine is a name sellers use for YK-11, and UK Anti-Doping lists the compound as YK-11 (Myostine) among prohibited SARMs. A product name says nothing about what a capsule contains; only a batch certificate with an identity result matching C25H34O6, molecular weight 430.5, can show that. Free Muscle sells YK-11 under its code name; every batch is assayed by Janoshik Analytical, and it is supplied for laboratory research only.
Is YK-11 really a myostatin inhibitor?
Only as a hypothesis. The label comes from a 2013 cell study in which YK-11 induced follistatin, a protein that neutralises myostatin, in mouse myoblasts. A 2021 study in mice with sepsis also described YK-11 as a myostatin inhibitor and reported lower inflammation and fewer deaths in treated animals. No study has examined it in people, so for humans the myostatin label is unproven.
Has YK-11 been tested in humans?
No, not in a clinical trial. None has been published, and none was registered on ClinicalTrials.gov when we checked in October 2026. The in vivo data come from a 2021 mouse sepsis study, rat studies of the hippocampus in 2023 and 2024, a 2025 rat bone-defect study and doping-control work that traced its urinary metabolites, including studies in horses. No human safety or efficacy data exist.
How do I verify the batch of YK-11 I received?
It depends on the brand. Free Muscle YK-11 is Janoshik-assayed batch by batch, and emailing us the batch number from your container gets you the certificate for that lot; compare the lot number with your label and read the identity and purity lines. iMuscle YK-11 carries a certificate on its listing only when iMuscle has supplied one for the batch we hold. Our lab tests page explains how to read either.
Is YK-11 detectable in sports drug testing?
Yes. YK-11 is one of the SARMs named in S1.2 of the 2026 WADA Prohibited List, so it is prohibited at all times. The Cologne anti-doping laboratory identified fourteen urinary metabolites and added two to routine screening; intact YK-11 is not excreted, but conjugated metabolites stayed traceable for more than 48 hours. In 2024 the UCLA Olympic Analytical Laboratory reported YK-11 in a doping control sample. Anyone subject to anti-doping rules should treat it as prohibited.
Which strength of YK-11 should I choose?
We do not advise on strength, quantity or use. YK-11 is sold for laboratory research only, and the appropriate material depends on the research protocol. Both listings on this page are 10mg per capsule with 60 capsules, so total milligrams are identical and the comparison is cost per milligram and COA status. Nothing on this site is dosing or medical advice.
How is YK-11 shipped, and can I return it?
Delivery within the UK is free and tracked, and every YK-11 order leaves in plain packaging. Orders placed before 2pm on a working day are processed that day, while EU deliveries take 3 to 7 working days. Unopened products may be returned within 30 days under our guarantee, and all buyers must be 18 or over. Full terms are on the shipping and guarantee pages.
Where can I buy YK-11 in the UK?
On this page you can compare every YK-11 listing we stock, from Free Muscle and iMuscle. Every UK order ships free with tracking, with no minimum spend, and usually arrives 2-3 working days after dispatch. Everything here is supplied for laboratory research use only, not for human consumption, to adults aged 18 or over.
Do you deliver to Romania and the rest of the EU?
Yes. Orders to Romania and other EU countries travel by our paid, tracked international service and usually arrive 3-7 working days after dispatch; delivery to the rest of the world usually takes 5-14 working days. Prices are in pounds sterling (GBP). Rules differ in other countries, so check local law before ordering for delivery abroad.
Is there a discount when I buy more than one?
Yes, on Free Muscle-brand products: 5% off automatically when your cart holds 2 of them and 10% off with 3 or more, applied in the cart. The offers do not combine. Products from the other brands on this page are not included.