What is Boldenone Boldenone is a synthetic steroid drug, which is mainly used to treat muscular atrophy and anemia of horses, and is also used by athletes and fitness enthusiasts to increase muscle mass and strength.oldenone usually exists in two forms: Boldenone Undecellenate and Boldenone Acetate. Boldenone is a kind of testosterone steroid drugs, which is similar to testosterone in …