YK-11

YK-11, also written YK11 and known chemically as (17alpha,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester, is a steroidal compound 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 comes from a single 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. This has not been shown in any animal or human. 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.

What the published research reports

Identification as an AR partial agonist (2011). Kanno and colleagues showed in an androgen-response-element luciferase assay that YK11 was a partial agonist of the AR, accelerated its nuclear translocation, did not induce the N/C interaction and blocked DHT from doing so. Gene expression effects in MDA-MB 453 cells varied by gene context, leading the authors to propose SARM-like behaviour. This is an in vitro study.

Myogenic differentiation and follistatin (2013). The same group reported that YK11 induced myogenic differentiation of C2C12 myoblasts, with stronger induction of MyoD, Myf5 and myogenin than DHT. YK11, but not DHT, induced follistatin expression, and an anti-follistatin antibody reversed the effect. Again a cell-culture result only.

Osteoblast proliferation (2018). Yatsu and colleagues found that YK11 and DHT accelerated proliferation and mineralisation of MC3T3-E1 mouse osteoblast cells, increased osteoprotegerin and osteocalcin, and raised phosphorylated Akt, effects attenuated by an AR antagonist.

Metabolism and detection for doping control (2018). Piper and colleagues, at the Cologne anti-doping laboratory, identified YK11 in a seized black-market product and conducted an elimination study with deuterium-labelled YK11. Fourteen urinary metabolites were detected; no intact YK11 was found in urine, but glucuronidated and sulfated metabolites remained traceable for more than 48 hours, and two were incorporated into routine anabolic-agent screening.

Hippocampal effects in rats (2024). Dahleh and colleagues gave rats YK11 for five weeks with or without swimming exercise. YK11 downregulated BDNF/TrkB/CREB signalling in the hippocampus, increased the pro-inflammatory cytokines IL-1beta and IL-6, reduced IL-10, raised p38 MAPK activity and activated the Bax/Bcl-2/caspase-3 apoptotic cascade, with impaired aversive memory consolidation. Exercise partly offset some of these changes.

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.
• Free Muscle Research Bundle (MK-677, RAD-140 and YK-11). Three Free Muscle-brand compounds sold together for laboratory work, each from a Janoshik-assayed batch. View the research bundle (not listed at the moment; see the Free Muscle range).

How to compare them

Both single-compound listings contain 600mg per pack (10mg multiplied by 60 capsules), so the quantity is identical and the comparison comes down to cost per milligram and testing. Divide each pack price by 600 to get cost per milligram. Then weigh the certificate: the Free Muscle batch has a Janoshik identity and purity assay available for its lot number, while the iMuscle batch carries a COA only where the manufacturer has supplied one. Given that YK-11 was first identified by anti-doping scientists in an unlabelled black-market product, 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

A certificate of analysis (COA) answers the two questions that matter about a YK-11 capsule: is the compound what the label says, and how much is present. A genuine batch certificate is issued by an independent laboratory, names the lot number, and reports identity (by HPLC or mass spectrometry against a reference standard) and assayed purity or content.

Every Free Muscle-brand batch is assayed by Janoshik Analytical, an independent laboratory, and the certificate for the batch you receive is sent on request by email. For other brands we show a COA only where the manufacturer has supplied one for the batch we hold. A generic PDF with no batch number, or one dated long before the product was made, is not a batch certificate and tells you nothing about the capsules in your hand. Our lab tests page explains how to read a Janoshik certificate and match it to your batch.

Legal status in the UK

YK-11 is not a licensed medicine in the United Kingdom. It has never been granted a marketing authorisation by the MHRA, and it is not an authorised food supplement or a permitted novel food ingredient. It cannot legally be sold or labelled for human consumption. Free Muscle sells YK-11 to adults aged 18 or over for laboratory and research purposes only, and every listing states this. YK-11 falls within section S1.2 of the World Anti-Doping Agency Prohibited List (Other Anabolic Agents), which covers all SARMs and substances with similar structure or effect, and is prohibited at all times; the Cologne laboratory has published detection methods for its metabolites. Anyone subject to anti-doping rules should treat any product in this class as prohibited at all times, in and out of competition. For a fuller overview of the class, see our research guide to SARMs.

Storage and handling

Keep YK-11 capsules in the original sealed container in a cool, dry place away from light and heat. Do not decant into unlabelled containers, and record the batch number so that a COA request can be matched to the exact material. Keep out of reach of children and pets, and follow standard laboratory good practice: gloves when handling, no eating or drinking in the work area, and disposal in line with local rules for research chemicals.

Delivery and returns

All orders are sent from Scunthorpe by FreeMuscle LTD, a UK company, 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?
• MK-677 (Ibutamoren): what the research says

Related collections: RAD-140 (Testolone), MK-677 (Ibutamoren), Bundles, all SARMs.

YK-11 is sold strictly for laboratory research use only. It is not a licensed medicine, has not been evaluated or approved by the MHRA, EMA or FDA, is not a food supplement and is not for human consumption. Buyers must be 18 or over. Nothing on this page is medical advice, dosing advice or a recommendation to use this compound in any way; the published findings summarised above describe study participants and laboratory models, not the products listed.

Research guides

• YK-11: a steroidal compound sold as a SARM, what is actually known