Boldenone (INN, BAN), also known as Δ1-testosterone, 1-dihydrotestosterone, or androsta-1,4-dien-3-one-17β-ol (train name Equipoise) is a long-acting injectable anabolic agent for horses, supplied in a vial providing 50 mg boldenone undecylenate per mL in sesame oil with 3% (w/v) benzyl alcohol as a preservative. The activity of boldenone is mainly anabolic, with a low androgenic potency. Boldenone will increase nitrogen retention, protein synthesis increases appetite and stimulates the release of erythropoietin in the kidneys. Boldenone was synthesized in an attempt to create a long-acting injectable methandrostenolone (Dianabol), for androgen deficiency disorders. Boldenone acts similar to methandrostenolone with fewer adverse androgenic effects. Although commonly compared to nandrolone, boldenone lacks progesterone receptor interaction and all the associated progestogenic side effects. Equipoise (Boldenone Undecylenate Injection) is recommended as an aid for treating debilitated horses when an improvement in weight, haircoat or general physical condition is desired. Debilitation often follows disease or may occur following overwork and overexertion. Boldenone improves the general state of debilitated horses, thus aiding in correcting weight losses and improving appetite. It is not a substitute for a well-balanced diet. Optimal results can be expected only when good management and feeding practices are utilized. Boldenone should be considered only as adjunctive therapy to other specific and supportive therapy for diseases, surgical cases, and traumatic injuries.