YK11 (CAS 1370003-76-1) is a high-purity selective androgen receptor modulator (SARM) API, featuring a unique steroidal structure that acts as a partial agonist of the androgen receptor. Unlike traditional androgens, it selectively targets skeletal muscle and bone tissue receptors, avoiding widespread systemic effects. In in vitro studies, it has shown stronger anabolic activity than dihydrotestosterone (DHT) in C2C12 myoblasts, effectively promoting muscle cell growth and inhibiting myostatin—a protein that limits muscle development.