Boldenone undecylenate is a veterinary drug used primarily in horses, dogs, and livestock to promote muscle growth and improve physical performance. It exerts its effects by binding to androgen receptors, triggering molecular events that regulate gene expression. This leads to increased protein synthesis and muscle growth. Boldenone undecylenate also has masculinizing effects on male sexual characteristics. Common side effects include changes in behavior, increased aggression, masculinization in female animals, and effects on the reproductive system. Its use as a veterinary drug is supervised by licensed professionals, but it is not approved in all countries and is illegal for human use.