Steroid sex hormone derived from cortisol and the primary androgen hormone is biologically produced by specialized cells located in the testes. In men, it is responsible for developing sexual organs and secondary sexual characteristics, such as the beard and the deep voice. Among its functions, there is also the mediation of sexual libido. Testosterone is the primary hormone prescribed in hormone therapy for FtM; in drug form, there are variants that act more physically like Testoviron or more mentally like Sustanon. Along with testosterone, antiestrogens are given because too much testosterone is converted into estrogen in women.