Disclaimer: I have no idea what I'm talking about. Here's roughly how it works, if I understand correctly. First, a normal male endocrine system looks roughly

Disclaimer: I have no idea what I'm talking about. Here's roughly how it works, if I understand correctly. First, a normal male endocrine system looks roughly like this: 1. The hypothalamus produces GnRH. 2. In response to stimulation by GnRH, the pituitary produces LH and FSH. 3. In response to FSH and LH, the testes produce sperm and testosterone, respectively. 4. Testosterone inhibits the production of GnRH by the hypothalamus (a negative feedback mechanism). This effectively keeps testosterone levels regulated. When external testosterone is introduced, here's what happens: 1. The increased testosterone inhibits the production of GnRH by the hypothalamus. 2. In absence of GnRH, the pituitary produces less FSH and LH. 3. In absence of FSH, the testes produce less sperm (this is the contraceptive effect). In absence of LH, the testes produce less testosterone. The net effect is less sperm and the body produces less testosterone on its own. This makes me wonder: would this lead to testicular atrophy? That happens with steroidal antiandrogens and GnRH agonists/antagonists, both of which have the effect of decreasing LH and FSH. Also, I think there are cardiovascular risks associated with high testosterone.