Deca Durabolin is one of the most popular injectable anabolic steroids available. The legal Deca steroid is used to treat osteoporosis and loss of bone density. What is Deca? Deca Durabolin (Nandrolone) has phenomenal anabolic and androgenic properties which makes it a favorite steroid among bodybuilders. The reason for nandrolone’s popularity is its effectiveness and efficacy in building strength and muscle.