Xenoestrogen
Xenoestrogens are clinically significant because they can mimic the effects of endogenous estrogen and thus have been implicated in precocious puberty and other disorders of the reproductive system.
Estrogen and neurodegenerative diseases
Nonsteroidal estrogens include xenoestrogens, phytoestrogens and mycoestrogens. They are very useful in neurodegenerative diseases' therapy when considering about the side effects caused by estradiol. 
As the development of chemical synthesis, it becomes possible for people to construct new molecules. Drug companies can exploit naturally existing compounds and synthetic compounds that have estrogen-like activity to produce patented proprietary drugs, especially the contraceptives. 
Phytoestrogens are plant derived estrogens and have similar structures with 17beta-estradiol thus may cause estrogenic or anti-estrogenic effects.