LGD-4033

LGD-4033 binds to the androgen receptor with high affinity (Ki of approximately 1 nM), functioning as a potent and selective agonist in muscle and bone tissue. Like other SARMs, its tissue selectivity is mediated by differential cofactor recruitment: upon binding to the AR, LGD-4033 induces a receptor conformation that preferentially recruits coactivators expressed in skeletal muscle and bone, while showing minimal agonist activity in androgen-sensitive tissues such as the prostate and skin. In preclinical studies, LGD-4033 produced dose-dependent increases in muscle mass (levator ani weight) with significantly less stimulation of prostate weight compared to testosterone. At the molecular level, AR activation by LGD-4033 drives gene transcription pathways involved in protein synthesis, nitrogen retention, and myogenic differentiation in skeletal muscle. The compound also promotes osteoblast activity and bone mineral density through AR signaling in bone tissue. LGD-4033 does not undergo aromatization to estrogen and is not a substrate for 5-alpha reductase, so it does not produce estrogenic side effects (gynecomastia, water retention from estrogen) or DHT-mediated side effects (prostate enlargement, androgenic alopecia). However, as a potent exogenous AR agonist, LGD-4033 suppresses endogenous testosterone production through negative feedback on the hypothalamic-pituitary-gonadal (HPG) axis in a dose-dependent manner. This suppression is generally considered more pronounced than that caused by Ostarine at equivalent effective doses, consistent with its greater AR binding affinity and anabolic potency.