Methyltestosterone is a synthetic androgen receptor agonist. Methyltestosterone is a testosterone mimic used for treating men with testosterone deficiency and related androgen replacement therapies. In addition, it is used in the treatment of breast cancer in postmenopausal women as an antineoplastic agent. Methyltestosterone is a testosterone derivative bearing a methyl group at the 17 alpha position that functionally increases bioavailability. Methyltestosterone binds cytosolic androgen receptors and the ligand-receptor complex functions as a transcription factor regulating the expression of androgen-responsive genes. Androgen responsive genes are responsible for the growth and development of male sex organs and male secondary sexual characteristics. Anabolic agents such as methyltestosterone stimulate anabolism and inhibit catabolism and thus stimulate the development of muscle mass, strength, and power.