Emerging peptide · Preclinical & theoretical

YK-11

A steroidal myostatin-pathway compound widely sold as a SARM with claimed follistatin-induction effects — minimal clinical research base.

Preclinical / non-medical

Investigational compounds — read carefully

This section covers peptides at the frontier of research. Most entries are preclinical, in early or mid-stage clinical trials, or theoretical. Evidence levels are explicitly marked on every entry.

Nothing on these pages constitutes medical advice, dosing recommendations, or instructions for use. Many of these compounds are not commercially available; some are not legal for human use. Decisions about treatment require a qualified clinician.

At a glance

A synthetic steroidal compound originally described in 2011 that has become widely sold in performance-enhancement markets under SARM branding. Marketed claims center on follistatin induction and partial androgen-receptor activity, but the human research base is essentially absent.

Class
Synthetic steroidal compound (often grouped with SARMs)
Sponsor
None — no commercial pharmaceutical development
Stage
Preclinical / non-medical use only
Lead claim
Follistatin induction and selective AR activity

What it is

YK-11 is a synthetic compound first described in academic publications by Kanno and colleagues in 2011 and 2013 as a novel selective androgen receptor modulator (SARM) with apparent follistatin-inducing properties in cell-culture systems. Despite the SARM branding, structurally YK-11 is a steroidal compound rather than the non-steroidal scaffold of the better-characterized SARM candidates (ostarine, ligandrol, RAD-140).

Current research status

YK-11 has no formal pharmaceutical development program. There are no clinical trials. The compound exists almost exclusively in the grey-market performance-enhancement supply chain, where it is marketed for muscle hypertrophy. Multiple anti-doping agencies (including WADA) classify it as a prohibited substance.

Mechanistic rationale

The 2011/2013 cell-culture work suggested two simultaneous mechanisms: partial agonism at the androgen receptor and induction of follistatin expression. Follistatin is an endogenous antagonist of myostatin and several related TGF-β ligands; if YK-11 reliably increases follistatin expression in vivo at achievable doses, the downstream effect would be partial relief of myostatin-mediated suppression of muscle growth — a complementary axis to direct AR activation. Whether these in-vitro findings translate to meaningful in-vivo effects at safe doses in humans has not been established.

Available evidence

Original cell-culture work (Kanno et al., Biol Pharm Bull 2011, 2013) — Reported partial AR agonism and follistatin induction in C2C12 myoblast cell lines.[1][2]

Human clinical research — Essentially absent. There are no published RCTs of YK-11 in humans for any indication.

Adverse event reports — Hepatotoxicity case reports have been published in users of grey-market products.[3]

Why it's interesting

YK-11 is interesting primarily as a case study in the gap between cell-culture mechanistic claims and validated clinical effects. The follistatin-induction hypothesis is conceptually attractive — it would represent a non-biologic route to partial myostatin pathway suppression — but the supporting evidence is two papers in a single cell line, with no in-vivo, animal, or human follow-up to validate that the effects translate.

Limitations & risks

The clinical evidence base is essentially zero. The marketing claims substantially outrun the underlying research. Hepatotoxicity case reports in users are part of the safety signal. Anti-doping agencies classify YK-11 as a prohibited substance, which is operationally relevant for any athlete subject to testing. The supply chain is grey-market, with no quality assurance on identity, purity, or contamination.

Community discussion notes

YK-11 is widely discussed in performance-enhancement and bodybuilding communities, often grouped alongside ostarine, ligandrol, and RAD-140 under the SARM umbrella. The community discussion frequently treats the 2011/2013 cell-culture findings as if they had been clinically validated; they have not.

The takeaway

YK-11 is an actively marketed grey-market compound with a minimal research base, hepatotoxicity case reports, and anti-doping prohibition. The follistatin-induction hypothesis is interesting in principle but not supported by clinical or even in-vivo animal data. For users interested in the underlying mechanism (myostatin pathway suppression via follistatin induction), the active research programs reside in the antibody and decoy-receptor space, not in YK-11.

References

  1. Kanno Y, et al. Selective androgen receptor modulator, YK-11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression. Biol Pharm Bull. 2013;36(9):1460-1465. https://pubmed.ncbi.nlm.nih.gov/23933180/
  2. Kanno Y, et al. (-)-17alpha-Methyl-11beta-hydroxyandrosta-1,4-dien-3-one (YK-11), a synthetic SARM, induces myogenic differentiation in C2C12 cells. Biol Pharm Bull. 2011;34(2):318-323. https://pubmed.ncbi.nlm.nih.gov/21415548/
  3. Flores JE, et al. Hepatotoxicity associated with selective androgen receptor modulators (SARMs): A case series. Clin Liver Dis. 2020;16(1):29-32. https://pubmed.ncbi.nlm.nih.gov/32714531/