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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

YK-11

Steroidal AR partial agonist marketed as a 'myostatin-inhibitor SARM'

Evidence grade 2 of 5, Thin. Read how the Atlas grades evidence.

The written rationale for this grade is still being prepared.

FDA
Not FDA approved; no human trials
WADA
Prohibited at all times (anabolic agent)

Reference only. Not medical advice.

What can go wrong

No human safety data exist. As a steroidal AR agonist it is expected to suppress endogenous testosterone and alter lipids, and users anecdotally report joint/tendon complaints; SARM-class hepatotoxicity concerns apply. Consumer products are frequently mislabeled. Banned in WADA sport.

This is something to take to a clinician. The Atlas can tell you what is known about yk-11 in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.

YK-11 is a synthetic compound based on a DHT (dihydrotestosterone) steroid backbone, marketed as a SARM and as a 'myostatin inhibitor.' In C2C12 muscle-cell studies it acted as a gene-selective partial AR agonist and upregulated follistatin (an endogenous myostatin antagonist). Despite heavy marketing of 'follistatin/myostatin' claims, there are no human clinical trials of YK-11, and calling it a SARM is misleading, structurally it is a steroidal compound.

Marketed as a myostatin-crushing SARM, but it is a synthetic steroid with no human data.

What people take it for

These are the reasons people give for taking it. They are not effects it has been shown to have.

  • Marketed (illegally) for muscle growth via 'myostatin inhibition'

How it is supposed to work

In cultured C2C12 myoblasts, YK-11 acted as a partial AR agonist and increased follistatin expression; follistatin binds and antagonizes myostatin, a negative regulator of muscle growth. This is the basis for its 'myostatin inhibitor' marketing. Because it is a steroidal AR-active compound, it would also be expected to suppress the HPT axis.

Cell-dish data, not a human drug

Every headline 'myostatin/follistatin' claim for YK-11 traces to in-vitro myoblast experiments (Kanno and colleagues). There are no pharmacokinetic, safety, or efficacy trials in humans or even good in-vivo data. Marketing it as a 'SARM' also obscures that it is structurally a synthetic steroid, with the liability profile that implies.

Safety in detail

YK-11 is an unapproved synthetic steroidal compound with zero human trial data. Its 'myostatin inhibitor SARM' marketing rests entirely on cell-culture experiments. Self-administration carries unquantified but plausible endocrine and hepatic risk.

Replacement is not the same as a cycle

No validated human dose exists; any consumer dosing is pure extrapolation from cell studies, making risk unquantifiable.

What it does to fertility

As a steroidal AR agonist it is expected to suppress LH/FSH and endogenous testosterone and impair spermatogenesis, but no human data exist.

What has to be monitored

The bloodwork this needs, and the reason it belongs with a clinician rather than a website.

  • Total/free testosterone, LH, FSH
  • Liver function tests
  • Lipid panel

What people get wrong

  • Often saidYK-11 is a SARM

    ActuallyStructurally it is a DHT-based synthetic steroid; classifying it as a SARM is misleading.

  • Often saidIt inhibits myostatin so it beats natural limits

    ActuallyThe only support is in-vitro follistatin data in cultured cells; there are no human trials establishing this effect or its safety.

Who profits, and who pushes back

Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.

How we got here

YK-11 was characterized by Yuichiro Kanno and colleagues in Japan in the early 2010s in a series of cell-based studies. It has never had a corporate clinical development program. Its reputation is almost entirely a product of internet bodybuilding marketing built on those in-vitro findings.

  1. 2011-2013Kanno et al. characterize YK-11 as a partial AR agonist in cells
  2. 2015Follistatin-induction cell study published
  3. Late 2010sMarketed online as a 'myostatin inhibitor SARM'

At a glance

Structure
DHT-based synthetic steroid
Claimed mechanism
Follistatin upregulation / partial AR agonist
Human trials
None
Key data
C2C12 myoblast cell studies (Kanno et al.)

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about YK-11. A short entry is not a safe entry.

  • Cost and market. We have not documented what it sells for or who sells it.
  • Supply chain. We have not mapped where it is made.
  • Who uses it. We have not documented the user groups.
  • What could change. No forward-looking summary yet.
  • How it compares. We have not set it against the alternatives.
  • Children and teenagers. We have not checked what is known about younger people.

Sources

The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.

The studies that matter

  • Kanno et al., YK-11 as gene-selective partial AR agonist (C2C12 cells)2013

    Partial AR agonism distinct from DHT; basis for 'selective' claim

  • Kanno et al., follistatin induction in myoblasts2015

    YK-11 upregulated follistatin mRNA/protein, driving myogenic differentiation in cells