ESR1
ESR1 estrogen receptor alpha — the molecular target that 4 compounds in the wiki act on.
In one line: The oestrogen receptor — key to female health, and to managing oestrogen in men on hormones.
ESR1 is the main oestrogen receptor. In women, oestrogen acting here governs the menstrual cycle, bone density, and much of menopausal health — which is why hormone replacement therapy works through it.
It matters for men too. When testosterone is high (from therapy or steroids), some of it converts to oestrogen, which acts here. Drugs called SERMs (like tamoxifen) block this receptor in specific tissues — used to prevent breast-tissue growth in men on steroids, and to restart the body's own testosterone. Other drugs (aromatase inhibitors) cut oestrogen production upstream instead.
The lesson: oestrogen isn't just a "female" hormone — men need some too, and crashing it causes as many problems as having too much.