YK-11
updated
YK-11 is a steroidal small molecule, not a peptide, that partially activates the androgen receptor. People take it for muscle and strength, and it is marketed as a myostatin blocker. In mouse muscle cells it showed partial androgen activity and raised follistatin, but direct myostatin blockade was never shown, and the human record is urinary metabolite and doping-detection work, with no trial of muscle, strength or safety. Graded F for cell and animal findings without controlled human evidence; rat studies raise neurological concerns, and FDA treats marketed products as unapproved new drugs.
steroidal androgen-receptor partial agonist
- Steroidal 19-norpregnane structure
- Partial androgen-receptor agonist in cells
- Follistatin expression is not direct myostatin blockade
- Human records concern detection, not efficacy
What exactly is YK-11?
YK-11 is a steroidal 19-norpregnane small molecule and androgen-receptor partial agonist. It is not a peptide and is not accurately described as a 17-alpha-methylated DHT peptide derivative.
source: PubChem · steroidal identity, National Center for Biotechnology Information PubChem, CID 119058028.
source: 2011 cell study · partial agonist, Kanno Y et al. Biological and Pharmaceutical Bulletin, 2011.
Has YK-11 built muscle or strength in people?
The cited PubMed and ClinicalTrials.gov records contain no controlled human efficacy trial. Human publications document urinary metabolites and one doping-control sample, not muscle, strength, body composition, function, or safety.
source: PubMed/ClinicalTrials.gov · no controlled efficacy trial, ClinicalTrials.gov search of the intervention-name and brief-title fields for YK-11 and YK11, with a PubMed search, run on 8 September 2026.
source: Human metabolism · count and route unstated, Piper T et al. Drug Testing and Analysis, 2018.
source: One sample · exposure detection only, Sobolevsky T et al. Drug Testing and Analysis, 2024.
Does YK-11 block myostatin?
Direct myostatin binding or systemic blockade was not shown. One mouse-myoblast study measured increased follistatin expression and cell differentiation. That laboratory step does not establish human myostatin inhibition or muscle growth.
source: Mouse-cell study · follistatin expression, Kanno Y et al. Biological and Pharmaceutical Bulletin, 2013.
What is the human half-life?
The human elimination paper reports metabolite detection windows but no parent concentration-time curve or half-life. Its public abstract also omits participant count and route. Detection of a metabolite beyond 48 hours does not mean a 48-hour parent half-life.
What safety signals exist?
The cited controlled human studies provide no side-effect rates. A mixed-exposure liver case cannot isolate YK-11, rat studies raise neurological concerns without defining human risk, and FDA found an undeclared anabolic steroid in one labeled product.
source: Case report · YK-11 plus LGD-4033 and RAD-140, Military Medicine, 2022.
source: Rat study · neurological injury signal, Dahleh MMM et al. Journal of Steroid Biochemistry and Molecular Biology, 2023.
source: FDA · undeclared trendione in one YK-11 product, US Food and Drug Administration, updated December 2025.
source: PubMed/ClinicalTrials.gov · no controlled efficacy trial
Is YK-11 approved, legal, or permitted in sport?
FDA identifies marketed YK-11 products as unapproved new drugs, and WADA prohibits YK-11 for covered athletes. These sources cover FDA enforcement and sports rules; they do not establish the legality of possession in a particular jurisdiction.
source: FDA 2025 · YK-11 capsule claims, US Food and Drug Administration, 12 December 2025.
source: FDA · undeclared trendione in one YK-11 product
source: WADA 2026 · YK-11 prohibited, World Anti-Doping Agency, effective 1 January 2026.
Studies and sources
PubChem · steroidal identity
Official chemical database record
National Center for Biotechnology Information PubChem, CID 119058028.
PubChem identifies YK-11 as a C25H34O6 small molecule with a 19-norpregnane steroidal core and a C17/C20 spiroketal. It has no amino-acid sequence and is not a peptide.
Read the original source2011 cell study · partial agonist
Cell study
Kanno Y et al. Biological and Pharmaceutical Bulletin, 2011.
YK-11 showed partial androgen-receptor agonist behavior in reporter and MDA-MB-453 cell systems. The experiment did not measure human muscle, strength, body composition, or safety.
- Study design
- In vitro receptor and cell assay
Mouse-cell study · follistatin expression
Mouse-cell study
Kanno Y et al. Biological and Pharmaceutical Bulletin, 2013.
In C2C12 mouse myoblasts, YK-11 produced weaker androgen-receptor signaling than dihydrotestosterone, increased follistatin expression, and promoted myogenic differentiation. The study did not test direct myostatin binding, systemic myostatin blockade, or a human muscle outcome.
- Participants / model
- C2C12 mouse myoblast cells
- Treatment
- Laboratory YK-11 exposure
- Study design
- In vitro cell experiment
Human metabolism · count and route unstated
Human analytical administration study
Piper T et al. Drug Testing and Analysis, 2018.
The study identified 14 urinary metabolites after administration of six-fold deuterated YK-11. Unconjugated metabolites disappeared within 24 hours and conjugated metabolites remained detectable beyond 48 hours. The public abstract does not state participant count or route and does not report parent concentration-time data, efficacy, or safety.
- Participants / model
- Post-administration human urine specimens; participant count not stated in the public abstract
- Treatment
- Six-fold deuterated YK-11; route not stated in the public abstract
- Study design
- Human analytical elimination experiment
A metabolite detection window is not the parent drug’s half-life.
Read the original sourceOne sample · exposure detection only
Human analytical case report
Sobolevsky T et al. Drug Testing and Analysis, 2024.
Investigators detected YK-11 and metabolites in one doping-control sample. The report documents exposure but provides no efficacy, dose-response, safety, route, or parent pharmacokinetic result.
- Participants / model
- One human doping-control sample
- Study design
- Analytical case report
PubMed/ClinicalTrials.gov · no controlled efficacy trial
Registry and literature record
ClinicalTrials.gov search of the intervention-name and brief-title fields for YK-11 and YK11, with a PubMed search, run on 8 September 2026.
The cited PubMed and ClinicalTrials.gov records contain no human administration, pharmacokinetic, safety, or efficacy study for YK-11.
Case report · YK-11 plus LGD-4033 and RAD-140
Human adverse-event case report
Military Medicine, 2022.
The report describes cholestatic liver injury after combined exposure to products labeled YK-11, LGD-4033, and RAD-140. It supports a serious warning about the exposure pattern but cannot identify which substance, contaminant, or combination caused the injury.
- Participants / model
- One person with multi-product exposure
- Study design
- Case report
Single-compound causality cannot be assigned.
Read the original sourceRat study · neurological injury signal
Animal study
Dahleh MMM et al. Journal of Steroid Biochemistry and Molecular Biology, 2023.
The study reported oxidative-stress and mitochondrial-injury signals in rat hippocampus after YK-11 exposure. Publicly reported dose-unit inconsistencies block a human exposure comparison.
- Participants / model
- Rats
- Treatment
- Experimental YK-11 exposure
- Study design
- Animal toxicology study
FDA 2025 · YK-11 capsule claims
FDA warning letter
US Food and Drug Administration, 12 December 2025.
FDA identified YK-11 capsules marketed with muscle and myostatin claims as unapproved new drugs. The seller’s claims are evidence of marketing, not proof that YK-11 works or that the capsules contained the stated amount.
Read the original sourceFDA · undeclared trendione in one YK-11 product
FDA safety and testing communication
US Food and Drug Administration, updated December 2025.
FDA reports finding undeclared trendione, an anabolic steroid, in one product labeled to contain YK-11. The finding concerns one tested product.
The agency also describes class-level SARM risks without providing YK-11-specific incidence.
Read the original sourceWADA 2026 · YK-11 prohibited
Sports rule
World Anti-Doping Agency, effective 1 January 2026.
YK-11 is prohibited under S1.2 other anabolic agents for athletes governed by the World Anti-Doping Code.
Read the original sourceWhy is YK-11 in F tier?
F tier reflects cell and animal findings without controlled human evidence for muscle gain, strength or safety. The human publications identified concern exposure detection and metabolism.
how tiers are graded: methodology · every cited source · about reptides.
Research reference, not medical advice. Entries distinguish product labels, study doses and reported protocols. Check the linked source for the product, route and population.