YK-11

a steroidal androgen-receptor research chemical with cell and animal findings, no controlled human trial, no measured half-life, and no established human safety margin.

tier F · androgens · 0 controlled human trials

verdict

the androgen-receptor signal is real in cells, but the human evidence file is empty and the safety file contains unresolved animal toxicity and case-level warning signals.

if you're asking whether YK-11 is a peptide or a 17-alpha-methylated DHT derivative — neither description is correct. YK-11 is a steroidal small molecule with a 19-norpregnane skeleton and a C17/C20 spiroketal. it is not a peptide, it has no free 17-beta hydroxyl, and it does not carry the alpha-face methyl group that defines a 17-alpha-alkylated oral androgen.

if you're asking whether it builds muscle in people — no controlled human body-composition or strength trial was located. the 2013 C2C12 mouse-myoblast study reported partial androgen-receptor agonism plus increased follistatin expression. that is a mechanism signal, not a human muscle outcome.

if you're asking what its half-life is — no concentration-time study has measured one in humans or animals. horse studies identified YK-11 and its metabolites after oral exposure, but detection and metabolite identification are not terminal half-life measurements. the page therefore publishes no number.

if you're asking whether the safety concern is only theoretical — the concern is broader than theory but attribution remains limited. rat studies report hippocampal oxidative, mitochondrial, inflammatory, apoptotic, and memory signals. one human cholestatic-injury case involved YK-11 alongside other SARMs, so it cannot establish that YK-11 alone caused the injury.

animal exposure is shown as animal evidence only. it is not a dose, protocol, or human-equivalent-dose calculation.

why F-tier

F-tier is the safety and evidence verdict. YK-11 has no phase 1 trial, no human efficacy or pharmacokinetic record, no established safe exposure, and animal neurologic warning signals under an unresolved dose record. The F does not mean inactive. It means the site cannot cross the identity, evidence, and safety gaps with class defaults or market claims.

the core tension

The molecule has a defined structure and reproducible androgen-receptor activity in cells. It also has zero controlled human trials, no measured half-life in any species, unresolved rat-dose reporting, and no way to separate YK-11 from co-exposures in the human harm reports.

what it is

YK-11 is a synthetic steroidal small molecule and partial androgen-receptor agonist. Its PubChem record is C25H34O6 at 430.5 Da, CAS 1370003-76-1, with a 19-norpregnane core and a C17/C20 methoxyethylidene spiroketal. It is commonly grouped with SARMs because of its intended receptor selectivity, but that market category does not make it nonsteroidal or clinically characterized.

what it does

In C2C12 mouse myoblasts, YK-11 activated androgen-receptor signaling less strongly than dihydrotestosterone and increased follistatin expression. Later animal papers investigated sepsis markers, equine metabolism and detection, and rat hippocampal toxicity. None measured human strength, lean mass, cardiovascular risk, endocrine suppression, or a terminal elimination half-life.

origin

The first indexed androgen-receptor pharmacology paper appeared in 2011. A 2013 C2C12 myoblast paper added the follistatin and myogenic-differentiation findings. The later record is a small and heterogeneous set of cell, mouse, rat, and equine studies rather than a drug-development program. No phase 1 trial or regulator-reviewed clinical dossier was located.

why researchers are interested

The appeal comes from a simple story: androgen-receptor activity combined with a reported follistatin signal. That story compresses a cell experiment into a human performance claim. The published record does not establish a human anabolic effect, a safe exposure, or even the basic pharmacokinetic curve needed to describe duration.

does it work

It has measurable activity in cells. That is the strongest defensible conclusion. There is no controlled human efficacy study, no human pharmacokinetic study, and no compound-specific human safety study. F-tier reflects failure of the human-evidence and safety thresholds, not a claim that the molecule is pharmacologically inactive.

claims vs the data

• YK-11 is a peptide — contradicted — it is a 430.5 Da steroidal small molecule with no amino-acid sequence.
• YK-11 is a 17-alpha-methylated DHT derivative — contradicted — the exact structure is a 19-norpregnane C17/C20 spiroketal and does not carry that structural feature set.
• YK-11 increases follistatin — preclinical — reported in C2C12 mouse myoblasts in one 2013 paper; no human tissue or clinical outcome confirms it.
• YK-11 has a known oral half-life — unsupported — no human or animal concentration-time half-life was located. equine detection and metabolite work cannot supply the number.
• YK-11 caused the published human liver injury — unresolved — the case involved several SARMs, including YK-11. it supports a serious mixed-exposure warning but cannot attribute causality to one ingredient.

key facts

• molecular formula: C25H34O6
• molecular weight: 430.5 g/mol
• amino acids: n/a (steroidal small molecule, not a peptide)
• half-life: unknown; no measured concentration-time half-life in humans or animals
• type: steroidal androgen-receptor partial agonist; SARM-adjacent research chemical
• CAS: 1370003-76-1
• 0 controlled human trials
• 0 measured half-life studies
• 3 unambiguous animal exposure records shown
• 2011 first indexed receptor paper

frequently asked questions

What is YK-11?

YK-11 is a synthetic steroidal androgen-receptor research chemical. It is commonly marketed beside SARMs, but it is not a peptide and not a clinically developed medicine.

Is YK-11 a 17-alpha-alkylated DHT derivative?

No. Its published structure has a 19-norpregnane core and a C17/C20 spiroketal, not the alpha-face C17 alkyl group or free 17-beta hydroxyl that description implies.

Does YK-11 increase follistatin?

One 2013 study reported increased follistatin expression in C2C12 mouse myoblasts. That is a cell-culture result and does not establish a human muscle, strength, or myostatin outcome.

What is the half-life of YK-11?

Unknown. No human or animal concentration-time study reporting terminal elimination half-life was located. Metabolite or hair detection cannot be converted into a half-life.

Is YK-11 safe?

No safe human exposure has been established. Rat work reports neurologic toxicity signals, while human concern is limited to mixed-exposure case reports and spontaneous reports that cannot isolate causality. Gray-market identity and purity add risk.

Is YK-11 approved?

No approved drug was located. YK-11 is not specifically named in DEA's current published alphabetical list, but DEA says that list is not comprehensive and 21 U.S.C. section 802(41) can cover qualifying unlisted anabolic steroids. Whether those broader provisions apply to YK-11 requires a fact- and jurisdiction-specific legal determination. It is prohibited in sport under WADA's other-anabolic-agents category.

related peptides

• testosterone — the clinically characterized androgen comparator
• Nandrolone — another 19-nor androgen with a human record
• Trenbolone — a non-human-approved androgen with major evidence gaps

reptides grades the research record and cites the literature behind every call. research reference only; not medical advice.