YK-11 SARM Guide: Follistatin, Myostatin and Research

YK-11 is an experimental steroidal compound that acts as a partial agonist of the androgen receptor. It is commonly described as a selective androgen receptor modulator, or SARM, and became well known because laboratory research reported increased follistatin expression in cultured muscle cells.

What Is YK-11?

YK-11 is a synthetic steroidal compound first described in published androgen-receptor research in 2011. Its molecular structure differs from nonsteroidal SARMs such as Ostarine, LGD-4033 and RAD-140.

The original study characterized YK-11 as a partial agonist of the androgen receptor. This means that it activates the receptor but does not produce exactly the same receptor response as a full agonist such as dihydrotestosterone.

YK-11 remains experimental and has not been approved as a muscle-building, bodybuilding or athletic-performance medicine.

Is YK-11 a SARM?

YK-11 is commonly classified as a SARM because laboratory research found that it produced selective, gene-dependent activity through the androgen receptor.

However, it is structurally different from many better-known nonsteroidal SARMs. YK-11 has a steroidal molecular structure, whereas Ostarine, LGD-4033 and RAD-140 are nonsteroidal compounds.

The SARM label therefore describes its proposed selective androgen-receptor activity rather than meaning that it has the same structure, evidence base or effects as every other product in the category.

How Does YK-11 Interact With the Androgen Receptor?

The original laboratory research found that YK-11 accelerated movement of the androgen receptor into the cell nucleus and activated androgen-responsive genes.

Unlike a full androgen-receptor agonist, YK-11 did not produce the same interaction between the receptor’s amino-terminal and ligand-binding regions. Researchers suggested that this difference helped explain its partial and gene-selective activity.

These findings came from laboratory assays and cultured cells. They do not establish how strongly YK-11 activates androgen receptors in healthy people or how that activity compares with testosterone in the human body.

YK-11, Follistatin and Myostatin

Much of YK-11’s reputation comes from a 2013 study involving C2C12 mouse muscle cells. Researchers found that YK-11 increased the expression of follistatin and several factors involved in muscle-cell differentiation.

Follistatin interacts with signalling proteins that include myostatin and activins. Myostatin normally helps regulate and limit skeletal-muscle growth.

When researchers used an antibody to block follistatin, the YK-11-related muscle-cell differentiation was reduced. This suggested that follistatin played an important role in the cellular response observed in the experiment.

Is YK-11 a Proven Myostatin Inhibitor?

YK-11 is frequently marketed as a myostatin inhibitor, but the established evidence requires more careful wording.

The principal study showed that YK-11 increased follistatin expression in cultured mouse muscle cells. It did not demonstrate a quantified reduction in circulating myostatin in humans or prove that YK-11 produces exceptional muscle growth in people.

Describing YK-11 as a direct and clinically proven human myostatin inhibitor therefore goes beyond what the published research establishes.

Muscle-Cell Differentiation Research

The 2013 cell study reported increased expression of muscle-regulatory factors including MyoD, Myf5 and myogenin during YK-11 treatment.

These proteins are involved in the process through which precursor cells develop into mature muscle cells. The researchers also reported greater myogenic differentiation with YK-11 than with dihydrotestosterone under the conditions used in the experiment.

This does not mean that YK-11 has been proven superior to testosterone or dihydrotestosterone for increasing human muscle mass. Cultured-cell findings cannot determine real-world muscle growth, strength, absorption, metabolism or safety in people.

YK-11 and Bone-Cell Research

Separate laboratory research examined YK-11 in mouse osteoblast precursor cells. Osteoblasts are cells involved in the formation of bone tissue.

The researchers reported increased osteoblast proliferation and differentiation through androgen-receptor-dependent signalling.

This remains cellular research. It does not establish that YK-11 increases bone density, prevents fractures or treats osteoporosis in humans.

Animal Research Involving Muscle Wasting

A later study examined YK-11 in a mouse model of bacterial sepsis. Researchers evaluated muscle wasting, inflammation, organ markers and survival in the experimental animals.

The study reported reduced signs of muscle wasting and changes in inflammatory measurements in YK-11-treated mice.

This research involved experimentally induced sepsis in mice and very different exposure conditions from recreational SARM use. It cannot establish a bodybuilding protocol or predict equivalent effects in healthy people.

Has YK-11 Been Studied in Humans?

Detailed controlled human trials establishing YK-11’s effects on muscle mass, strength, body composition, hormonal suppression or long-term safety are not available in the published evidence reviewed for this guide.

Some anti-doping research has investigated how YK-11 is metabolized and detected, but metabolism studies are not clinical trials of effectiveness or safety.

This makes YK-11’s evidence base substantially weaker than compounds such as Ostarine and LGD-4033, which have published controlled human studies.

Why Muscle-Gain Claims Exceed the Evidence

YK-11 is often promoted online using claims such as exceptional muscle growth, steroid-like strength and strong myostatin inhibition.

Those claims are largely extrapolated from cultured-cell experiments, animal research and non-medical reports. There is no controlled human trial establishing a predictable amount of muscle or strength gain.

YK-11 should also not be described as producing testosterone-like results without detrimental effects. Human safety, hormonal effects and long-term outcomes have not been established.

YK-11 Cycle and Dosage Discussions

Various YK-11 amounts and cycle lengths are discussed in bodybuilding communities, but no clinically validated human dosage or performance protocol has been established.

The absence of human pharmacokinetic research also means that absorption, effective exposure and individual variability are not well characterized.

For those reasons, this guide does not present an online community dosage as an evidence-based recommendation.

Does YK-11 Require PCT?

YK-11 activates the androgen receptor and may affect normal hormonal signalling. However, controlled human studies have not quantified the degree of testosterone suppression or the typical recovery pattern.

It should not be assumed that YK-11 is non-suppressive simply because it is marketed as selective. The amount used, duration, additional compounds and individual hormone levels could all influence the response.

Blood testing provides more useful information than relying on cycle length or online claims. Current post-cycle products can be compared in the SARM PCT and Post-Cycle Support category.

YK-11 Compared With Ostarine

YK-11 and Ostarine both interact with androgen receptors, but their evidence bases differ significantly.

Ostarine MK-2866 has been evaluated in controlled human trials involving lean body mass and physical function. YK-11’s principal muscle-related evidence comes from cultured cells and animal research.

YK-11 is also steroidal in structure, while Ostarine is a nonsteroidal SARM.

YK-11 Compared With LGD-4033

LGD-4033 Ligandrol has a published placebo-controlled study in healthy men that measured lean body mass, hormone levels and lipid markers.

No equivalent controlled human trial has established YK-11’s body-composition or hormonal effects.

The two compounds should therefore not be compared solely through informal claims about which one is stronger.

YK-11 Compared With RAD-140

RAD-140 Testolone has entered human clinical research through an oncology development program, although it has not been validated through bodybuilding trials.

YK-11 has not developed a comparable published human clinical evidence base. Most YK-11 claims remain dependent on laboratory and animal research.

Why Sarms Thailand No Longer Stocks YK-11

Sarms Thailand no longer carries YK-11 as part of its active product range. This guide remains available so visitors and previous customers can access more accurate information about the compound and its research limitations.

Currently available products can be compared through the Liquid SARMs in Thailand category.

YK-11 Research and Anti-Doping Status

YK-11 remains an experimental compound without an approved bodybuilding or athletic-performance indication.

YK-11 is specifically named on the World Anti-Doping Agency Prohibited List under anabolic agents. Athletes subject to anti-doping testing should avoid products containing YK-11.

Frequently Asked Questions

Is YK-11 a steroid or a SARM?

YK-11 has a steroidal chemical structure and produces selective, partial activity through the androgen receptor. It is therefore commonly described as a steroidal SARM.

Does YK-11 inhibit myostatin?

Laboratory research found that YK-11 increased follistatin expression in cultured mouse muscle cells. This supports a possible relationship with myostatin signalling but does not establish clinically proven myostatin inhibition in humans.

Has YK-11 been tested in people?

No published controlled human performance trial has established its effects on muscle, strength, body composition, dosage or long-term safety.

Has YK-11 been proven stronger than testosterone?

No. Cultured-cell experiments cannot establish that YK-11 is stronger, safer or more effective than testosterone in the human body.

Does YK-11 cause muscle growth?

YK-11 promoted muscle-cell differentiation in laboratory research, but no controlled human trial has established a specific muscle-growth result.

Does YK-11 require SARM PCT?

Its androgen-receptor activity creates a reasonable concern about hormonal suppression, but the degree and recovery pattern have not been quantified through controlled human studies.

Can I still buy YK-11 from Sarms Thailand?

No. Sarms Thailand no longer stocks YK-11. The guide is retained for educational and historical product information.

YK-11 Research Sources

• Original research identifying YK-11 as an androgen-receptor partial agonist
• YK-11, follistatin expression and muscle-cell differentiation research
• YK-11 osteoblast proliferation and differentiation study
• YK-11 research in a mouse model of sepsis-related muscle wasting
• Research on YK-11-dependent androgen-receptor gene expression
• PubChem compound information for YK-11
• World Anti-Doping Agency Prohibited List