Wikipedia
Miroestrol is a phytoestrogen, a plant-derived chemical that mimics the biological activity of the hormone estrogen. Miroestrol was first reportedly isolated from the Thai herb Pueraria mirifica in 1960 and thought to be responsible for the supposed rejuvenating properties of the plant. However, more recent studies have suggested that the active ingredient may actually be the closely related chemical compound deoxymiroestrol (shown below), and the reported presence of miroestrol may only have been an artifact of the isolation procedure. When deoxymiroestrol is exposed to the oxygen in air, it is converted to miroestrol.
A comparative study of the estrogenic properties of phytoestrogens found that both deoxymiroestrol and miroestrol were comparable in activity in vitro to other known phytoestrogens such as coumestrol as 17β-oestradiol agonists. Because of their estrogenic activities, miroestrol, deoxymiroestrol, and other related compounds have been the targets of scientific research including total synthesis.
Extracts of Pueraria mirifica reportedly containing miroestrol are marketed as dietary supplements intended to lead to breast enhancement in women. However, there is no scientific basis for such claims. The Federal Trade Commission has taken legal action against marketers for these fraudulent claims.