IGF-1 is a growth factor that is closely related to insulin. It carries the same amount of amino acids as insulin and as stated above, it is responsible for the anabolic reactions to GH. When IGF-1 is released by the liver, it then binds to IGF growth factors inside the cells, and causes the stimulation of cell growth. It has many positive effects as it increases nitrogen retention, protein synthesis, and it promotes the growth of new muscle cells, when enough protein is present. The addition of muscle cells is a benefit that IGF-1 brings to the table that anabolic steroids don’t. Anabolic steroids help to increase muscle cell growth, but play no part in cell duplication. This is where anabolic steroids can work very synergistically with IGF-1. While new muscle cells are added from IGF-1, these cells can expect to grow larger from anabolic steroids.