YK-11 is a synthetic steroidal selective androgen receptor modulator (SARM) that also acts via the myostatin/follistatin axis — an unusual dual-mechanism compound that sits at the boundary between traditional SARMs and myostatin-pathway research tools. Unlike the peptide compounds elsewhere in the VialTalk catalogue, YK-11 is a small-molecule steroid derivative, not a peptide. This monograph lays out its chemical identity, dual mechanism, the published research record, and the substantive regulatory considerations that distinguish it from research peptides.
Chemical identity and structure.
YK-11 is a synthetic steroidal small molecule, formally classed as a SARM. It is structurally distinct from the more numerous non-steroidal SARMs (Ostarine, LGD-4033, RAD-140) and shares its steroidal backbone with derivative-class anabolic steroids. The compound is supplied as a white-to-off-white crystalline solid, sparingly water-soluble, typically formulated for in-vitro research with solvent vehicles (DMSO, propylene glycol). Polymorph studies have been published characterising the solid-state forms used in research preparations.
Mechanism of action.
YK-11 has a dual published mechanism. First, it is a partial agonist of the androgen receptor (AR), characterised in receptor-binding studies — the SARM property that places it in the steroidal-SARM class. Second, and unusually, it induces expression of follistatin in C2C12 myoblasts, where YK-11-mediated myogenic differentiation has been demonstrated to depend on follistatin expression and is reversed by anti-follistatin antibody. Follistatin antagonises myostatin, so the net downstream effect in muscle is myostatin-pathway inhibition. Additional preclinical work has reported osteoblastic-proliferation effects in MC3T3-E1 cells.
Research applications and the evidence base.
Published YK-11 research is dominated by preclinical and in-vitro work: myogenic-differentiation models, osteoblast biology, AR receptor-pharmacology characterisation, and a small number of broader-pathway papers including a sepsis-prevention study. There are no completed Phase III human clinical trials of YK-11 — it is not in any registered pharmaceutical-development pipeline known to VialTalk.
Regulatory status.
YK-11 is not FDA-approved for any indication and is not in active pharmaceutical development. Like other SARMs, it is banned by the World Anti-Doping Agency (WADA) under category S1 (anabolic agents). The 2018 U.S. SARMs Control Act, where enacted, also places SARMs including YK-11 under heightened controls. Researchers using YK-11 in human-touching contexts should be aware that it is treated as a non-approved investigational compound by every major drug regulator known to VialTalk.
Research context.
YK-11 occupies a slot of its own in the SARM landscape — the steroidal SARM with a published follistatin-induction mechanism. Researchers studying SARM pharmacology generally use it alongside non-steroidal references (Ostarine, RAD-140) to dissect the AR-partial-agonism vs myostatin-pathway contributions to muscle-biology outcomes.
Storage and handling.
YK-11 powder is stable at room temperature when kept dry and protected from light. Solutions in organic solvents (DMSO, propylene glycol) should be refrigerated and protected from light; in aqueous vehicles solubility is limited and precipitation can occur.
Quality and COA considerations.
A meaningful COA should confirm identity via mass spectrometry and NMR, purity by HPLC (≥98% benchmark), and explicit disambiguation from related steroidal SARMs and anabolic-androgenic steroids — sequence/structure-mislabelling is a known issue across grey-market SARM supply.
Research-use note: This monograph is an educational summary of the published research literature on YK-11. The compound has not been evaluated in completed human clinical trials, has no FDA-approved indication, and is banned by WADA. Nothing here is medical advice or a usage recommendation.