YK-11

A steroidal molecule in a non-steroidal class

The word SARM was coined for non-steroidal ligands that bind the androgen receptor without the steroid nucleus and its metabolic liabilities. YK-11 is routinely sold under that label but does not meet that structural definition: it is a dihydrotestosterone derivative bearing an unusual C-17 gem-dimethyl malonate ester. The distinction matters when interpreting results, because a steroidal backbone can in principle interact with steroid-metabolising enzymes and steroid-binding proteins in ways a purely synthetic scaffold does not.

Partial agonism and the follistatin observation

The original characterisation described YK-11 as a partial agonist: it occupies the androgen receptor ligand-binding pocket but produces a lower maximal transcriptional response than a full agonist such as DHT, and can therefore compete with and blunt full-agonist signalling in the same system. Follow-up work in differentiating C2C12 mouse myotubes reported increased follistatin expression and markers of myogenic differentiation, with the effect described as androgen receptor dependent. Because follistatin binds and neutralises myostatin, this became the basis for the compound's reputation as a myostatin inhibitor — but no direct inhibition of myostatin has been demonstrated, and the finding rests on in-vitro data.

What has and has not been studied

• Androgen receptor binding and transactivation reporter assays in transfected cells
• Myotube differentiation and follistatin expression in the C2C12 line
• Anti-proliferative effects reported in some androgen-receptor-positive cancer cell lines
• No published controlled human trials; no systematic animal toxicology in the peer-reviewed record
• Analytical chemistry work developing detection methods for anti-doping laboratories

YK-11 has never been evaluated by a regulatory agency for any indication. The US FDA has publicly warned against SARM-labelled products and stated they do not qualify as dietary ingredients, and WADA prohibits the class at all times in sport. Independent analyses of consumer SARM products have repeatedly found mislabelling and adulteration, which is the practical reason lot-level analytical documentation is essential when the material is used as a reference standard or research input.

Store capsules in the original sealed bottle with the desiccant in place, at room temperature and away from heat, light and humidity; keep the research liquid upright, tightly closed and out of direct light, refrigerated if the study runs long. Note the lot number and the date the container is first opened so results remain traceable to the certificate of analysis. The compound is poorly water soluble, so aqueous work normally starts from a DMSO or ethanol stock diluted into medium — hold the final solvent fraction constant across every arm and include a vehicle-only control. Wear gloves, avoid raising dust from solid material, and dispose of waste under your institution's chemical hygiene plan.