Testosterone may be the most important single hormone that aging men need, and small quantities of testosterone precursors can provide a very important role for aging women too. It’s a fact that men manufacture small amounts of estrogen and women make small amounts of testosterone, but rather than their production taking place from specific glands, (i.e. the ovaries and the testes), in both sexes chemicals called aromatase convert testosterone to estrogen and vice-versa.
Medical testosterone replacement therapies have been very similar to estrogen replacement therapies in that the synthetic variants that have been used (and still are) are not from natural sources. They are similar to natural testosterone, but they do not duplicate the precise formula of natural human testosterone.