This page shows what was measured, who it was measured in, and what that does not settle.
What YK-11 does in the body
In mouse muscle precursor cells that partial activation switched on follistatin, a protein that blocks myostatin — and myostatin is the brake on muscle growth.
YK-11 is a steroid built around a slightly unusual chemistry: it turns the androgen receptor on, but only partly, and it does so without the receptor folding head-to-tail the way testosterone makes it fold. That is the whole basis of the claim that YK-11 is a myostatin inhibitor. It was measured in a dish, in mouse cells, in 2013, and it has never been measured in a person.
Why people take it. An unapproved research compound never tested in a person.
What happened in people
Three cell studies found partial activation of an androgen signal and one muscle-related protein change.
✓ Reviewed first-read answer
Where this came from
A person wrote this and a reviewer approved it against this exact record. It carries no effect size.
A reviewer approved this against this record. The reviewed-claim record carrying the exact population and effect size does not exist yet.
No source is stored against this line.
The limit that matters most
The muscle-growth claim comes from mouse cells in a dish, not animals or people.
Where it acts
Androgen receptor in skeletal myoblasts and osteoblasts, in cell culture
Kind of result
A step measured inside a person
Supervision
Professional supervision is normally required. It is a prescription or clinician-administered medicine where it is approved.
What the registries record it as
The substance registry classes this as chemical.
FDA substance registry · Z9748J6B0R · read 2026-08-29
The supplement label database classes it as other, under the name YK-11.
RNAWiki holds 3 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What it changes in the body◇Read from sources, not yet reviewed
The path through the body
From what a person takes to what changes. A solid line is a step measured in people. A dashed line is a step nobody has measured that way.
Start
YK-11
What a person takes: Oral capsule or powder; no established or studied human dose.
The measurement behind this step
Sold as a capsule or a bulk powder. There is no human dose because there has never been a human study. Any figure quoted as a dose for this compound has been extrapolated from cell-culture concentrations or from another compound entirely, and neither extrapolation is valid.
Getting in
Taken orally as a steroid of unknown human pharmacokinetics
Sold as a capsule or powder. How much of a dose reaches the blood, and how long it stays, has never been measured in a person.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
A 19-norpregnadiene with an orthoester at C17/C20. No human pharmacokinetic study exists. The metabolic fate after oral administration has been characterised in horses, where urinary and plasma metabolites were identified for doping control purposes.
Partially activates the receptor by an unusual route
It turns the receptor on only part of the way, and without the head-to-tail fold that testosterone causes.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Partial agonism at AR without the N-terminal/C-terminal interaction. Differential DNA binding and cofactor recruitment have been proposed as the determinants of the resulting gene expression profile, based on work in AR-positive breast cancer cells.
In mouse muscle precursor cells it switched on follistatin, which binds and blocks the growth-limiting protein myostatin.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
YK-11, unlike dihydrotestosterone, induced follistatin expression in C2C12 cells, with stronger induction of MyoD, Myf5 and myogenin than DHT; anti-follistatin antibody reversed the differentiation effect. No corresponding measurement of myostatin or follistatin exists in any whole animal or human given YK-11.
In the only in vivo study, a brain toxicity signal
The one experiment in living animals looked at the hippocampus and found oxidative stress and damaged mitochondria after five weeks.
╌╌Measured in animals. A result in animals says what to test next. It does not say what happens in people.
The measurement behind this step
Increased hippocampal oxidative stress and proteotoxicity with impairment of all measured mitochondrial function markers in rats over five weeks; exercise prevented some markers and did not reverse the respiratory chain or mitochondrial dynamics findings. There is no in vivo muscle outcome for this compound in any species.
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 5 steps from taking it to an effect in a person.
How we know it
Each step names the study behind it in the technical detail beside it.
What this does not prove
A change inside the body is a reason to look. It is not a result in a person.
Why it matters
A reader can see exactly where the chain stops being measured in people.
What we still do not know
No reviewed claim binds any of these steps to a named population.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
Nobody, under protocol. Outside protocol, people buying it as the strongest available SARM on the strength of the myostatin claim.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
Where the result stopped carrying
Molecular docking failed to predict its selectivity across five nuclear receptors when compared with measurement
No pharmaceutical sponsor has ever developed it, and no human trial has ever been registered
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
Other reasons RNAWiki checked and found nothing for (11)
It was studied for a different goal
The studies measured something else entirely. Nothing in this record points to this reason.
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Still being tested
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Oral capsule or powder; no established or studied human dose
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
Professional supervision is normally required. It is a prescription or clinician-administered medicine where it is approved.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
The identity record classes it as investigational; no register records an approval.
No source is stored against this line.
What is in the pack
Sold as a capsule or a bulk powder. There is no human dose because there has never been a human study. Any figure quoted as a dose for this compound has been extrapolated from cell-culture concentrations or from another compound entirely, and neither extrapolation is valid.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold and what that means for what is in the pack.
No source is stored against this line.
Where it is registered
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No register entry is recorded.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
No human safety data of any kind exist. The available toxicology is a five-week rat study showing hippocampal oxidative stress, proteotoxicity and impairment of every measured mitochondrial function marker. As a 19-norprogesterone derivative, progestogenic and other steroid receptor cross-reactivity is a structural possibility that the docking-versus-measurement study specifically shows cannot be resolved computationally. The androgen-receptor class effects — suppression of endogenous testosterone, reduced HDL cholesterol — apply by mechanism but have not been measured for this compound in anything.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear∅Nothing found in the sources checked
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Oral capsule or powder; no established or studied human dose
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
There is no human dose because there has never been a human study. Any figure quoted as a dose for this compound has been extrapolated from cell-culture concentrations or from another compound entirely, and neither extrapolation is valid.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on which forms are sold and how they compare.
No source is stored against this line.
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
This one is decided with a clinician, so this section holds questions to ask rather than a plan to run.
Self-experiment planning is not offered for a prescription or clinician-supervised medicine, investigational agent. The questions below are for a clinician or pharmacist.
Questions worth asking
Which of the trials of YK-11 studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki records evidence. It does not say whether this substance is right for you.
What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That YK-11 inhibits myostatin in a human being — the finding is follistatin induction in a mouse cell line, and no step downstream of it has been measured in any organism
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That it is the strongest SARM available, a ranking with no in vivo anabolic measurement in any species to support it
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That being a partial agonist makes it safer, when the only in vivo toxicology available shows brain mitochondrial dysfunction
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Formulation uncertainty
Several salts, forms or products of YK-11 are recorded. Results from one form may not transfer to another.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
What happened in people◇Read from sources, not yet reviewed
Check any of this yourself
Every line above traced back to the study it came from. This is the technical layer, and the vocabulary changes here.
Every line above can be traced to the study named beside it. Follow the link and read it.
It is a partial agonist that works without the N/C interaction
In plain words
The original 2011 paper established what YK-11 is: a compound that switches the androgen receptor partly on, using a different structural route from testosterone.
What was measured
Androgen receptor transactivation with and without the N/C interaction
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Kanno et al. characterised YK-11 as a partial agonist of the androgen receptor that activates the receptor without the N-terminal/C-terminal interaction — the intramolecular fold that full agonists such as dihydrotestosterone induce. This is a real, reproducible structural pharmacology finding and it is the only well-established fact about the compound. It describes what the molecule does to a receptor in a reporter assay. It does not describe what it does to a person, and the paper does not claim to.
Written into the record, not signed off as a reviewed claim
The follistatin result: mouse myoblasts, in a dish, in 2013
In plain words
In mouse muscle precursor cells, YK-11 switched on follistatin, and blocking follistatin with an antibody abolished the effect. This single experiment is the origin of every "myostatin inhibitor" claim about the compound.
What was measured
Follistatin expression and myogenic regulatory factor induction in C2C12 cells, with antibody reversal
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Kanno et al. treated C2C12 mouse myoblasts with YK-11 or dihydrotestosterone. Induction of the myogenic regulatory factors MyoD, Myf5 and myogenin was more marked with YK-11 than with DHT. YK-11, but not DHT, induced follistatin expression, and the YK-11-mediated differentiation was reversed by an anti-follistatin antibody. The authors conclude that follistatin induction is important for the anabolic effect of YK-11. Follistatin binds and inhibits myostatin, which is where the marketing term comes from. What is measured here is a mouse cell line differentiating in culture. It is not muscle growth, it is not in a mammal with a circulation, and it is not in a human.
Written into the record, not signed off as a reviewed claim
From a cell-culture follistatin signal to "myostatin inhibitor" in a product listing
In plain words
Being called a myostatin inhibitor implies the compound blocks the protein that limits muscle growth in the body. What was actually shown is that a mouse cell line made more of a follistatin protein in a dish.
What was measured
That YK-11 is a myostatin inhibitor in humans — a four-step inference from a single mouse-cell experiment, with no step after the first ever tested
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The chain of inference runs: YK-11 induces follistatin in C2C12 cells; follistatin binds myostatin; therefore YK-11 inhibits myostatin; therefore YK-11 removes the brake on muscle growth in humans. Every link after the first is unmeasured for this compound. No study has shown YK-11 reducing circulating or intramuscular myostatin in any animal, no study has shown it increasing muscle mass in any animal, and no study has given it to a human. Actual myostatin-pathway drugs — bimagrumab, landogrozumab, domagrozumab — were tested in humans and repeatedly increased lean mass without improving function, which is the same pattern seen with the SARMs, so even a successful inference would land somewhere less impressive than the marketing implies.
Written into the record, not signed off as a reviewed claim
In rats it produced hippocampal oxidative stress and mitochondrial dysfunction
In plain words
Five weeks of YK-11 in rats damaged the antioxidant systems and mitochondria of the hippocampus, a brain region used for memory. Swimming exercise protected against some of it but not most of it.
What was measured
Hippocampal antioxidant enzymes, mitochondrial respiratory chain markers and mitochondrial dynamics proteins after 5 weeks
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Dahleh et al. gave male Wistar rats YK-11 with or without a five-week swimming protocol. YK-11 altered the endogenous antioxidant system, increased oxidative stress and proteotoxic markers, and impaired all measured mitochondrial function markers in the hippocampus. Exercise alone was neuroprotective. In combination, exercise prevented some mitochondrial toxicity markers, including MnSOD/SOD2 and MTT reduction capacity, but did not reverse the increased oxidative stress or the dysfunction of the mitochondrial respiratory chain and mitochondrial dynamics proteins. A companion 2024 paper in Chemico-Biological Interactions extends the hippocampal findings. This is the only in vivo toxicology on the compound and it is in rats.
Written into the record, not signed off as a reviewed claim
Docking predictions of its selectivity did not hold up
In plain words
A 2026 study compared what computer models predicted about which receptors YK-11 binds with what measurement showed, and the predictions were wrong.
What was measured
Not recorded
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
A 2026 study in the International Journal of Molecular Sciences compared molecular docking predictions of SARM selectivity with measured activity across five nuclear receptors, using YK-11 and ostarine as the test cases, and reported that docking failed to predict selectivity. This is directly relevant to YK-11 because it is derived from 19-norprogesterone, so progesterone, glucocorticoid and mineralocorticoid receptor cross-reactivity is a live structural question rather than a hypothetical one, and the computational shortcut that a supplement vendor might invoke does not answer it.
Written into the record, not signed off as a reviewed claim
Confirmed in a human doping control sample for the first time in 2024
In plain words
The UCLA Olympic Analytical Laboratory published the first confirmed detection of YK-11 in an athlete's sample in 2024, which is the first documented human exposure of any kind.
What was measured
Confirmed identification in a human anti-doping sample
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Sobolevsky et al. at the UCLA Olympic Analytical Laboratory reported detection of YK-11 in a doping control sample. YK-11 also appears in validated LC-MS/MS screening methods for SARMs in dietary supplements, and in equine metabolism studies where the urinary and plasma metabolite profile after oral administration has been characterised. The notable point for a reference page is what this record consists of: the human data on this compound is entirely forensic. There is no pharmacokinetic study, no dose-finding, no safety observation — only the fact that laboratories can now identify it when someone has taken it.
This order is fixed in code and does not count clicks or time on the page.
What is not here
8 questions this page could not answer
These sections were prepared and left out because there was nothing to put in them. They are listed rather than hidden, so the gaps in this record are visible.
What was measured, goal by goal — found nothing in the sources checked.
How close this is to real life — found nothing in the sources checked.
Felt, measured, or meaningful — found nothing in the sources checked.
How long anything takes — found nothing in the sources checked.
What it may clash with — found nothing in the sources checked.
Other ways to the same goal — found nothing in the sources checked.
How this medicine reached us — found nothing in the sources checked.
What changed on this page — found nothing in the sources checked.
The record as stored
The full record, for auditing
Everything above is built from what is below. This layer keeps the technical vocabulary, record identifiers and every stored row, so a reader who wants to check the page can.
The older medicine-wide conclusion held in this record
Written for a clinical reader, and about the medicine as a whole rather than about one indication, population and set of trials. RNAWiki does not treat it as a programme conclusion and no reviewer has signed it off in that form. It is here word for word because it is what the record holds.
A steroidal androgen receptor partial agonist made as a structural probe, with three cell-culture papers and no human evidence whatsoever, marketed on a follistatin result obtained in mouse myoblasts and on nothing else.
Recorded evidence blocks (0)
Where it is registeredIdentifiers, relations and other names
✗ required summary fields resolved: 4 required field(s) not terminal: Why people use it, Best-supported result, Biggest unanswered question, Human evidence
✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 1 source rows
✓ no critical contamination: no quarantine open
✓ canonical metadata passed: slug and display name present
✓ no raw internal fields: enforced by the copy-contract test over the rendered page
This is a record of evidence. It is not medical advice, and it does not say this substance suits you. Nothing here says any substance on RNAWiki is appropriate for a child.