Here is an example, which is how most sex hormones work: 1. Your adult body produces enough testosterone to have 400-1200ng/dl testosterone in your blood strea

Here is an example, which is how most sex hormones work: 1. Your adult body produces enough testosterone to have 400-1200ng/dl testosterone in your blood stream. 2. You inject 100-150mg of testosterone ethanate into your muscles weekly. 3. Initially, that 100-150mg of exogenous testosterone puts your testosterone levels at around 1000-1800ng/dl. 4. Your pituitary detects this, and decreases the amount of luteinizing hormone released. This is a signaling hormone responsible for regulating the production of the testicles, among a few other things. 5. Your naturally testosterone production stops, dropping you to 400-1200ng/dl again. But now all exogenous. (this happened because your body detected you didn't need to make anymore) 6. Over time, since your testicles are not being used the cells atrophy and are catabolized. 7. You quit TRT, and are down to 0ng/dl 8. Over a few weeks of no testosterone, your body attempts to increase production but must regrow cells in the testicles. 9. Often this takes around 2 months to get up to a normal range again. You might get to 300-700ng/dl in those months, aka lower than before. 10. Over several more months nearly all men will recover full testosterone production and be back to normal. Some men however, in a rare case will not begin secreting LH again (secondary hypo) or will not be able to regrow the cells in their testicles to produce enough t again (primary hypo). The same feedback loops occur in progesterins, estrogens and other androgens. I believe the thyroid hormones T3 and T4 also have similar feedback loops.