An anabolic androgenic steroid that has gained huge acceptability among professional bodybuilders and athletes, Deca Durabolin or Nandrolone Decanoate is undoubtedly the second-best known injectable steroid after Testosterone.his steroid is generally used during mass gain or dieting phases and is one of the very few steroids that can be used in both the off-season and before a professional contest. Deca may also be used to dramatically improve protein synthesis, nitrogen retention, performance, and endurance.