Genistein belongs to the isoflavone class of flavonoids. It is also classified as a phytoestrogen, Phytoestrogens are plant-derived nonsteroidal compounds that posses estrogen-like biological activity. Genistein has been found to have both weak estrogenic and weak anti-estrogenic effects.

Genistein is the aglycone (aglucon) of genistin. The isoflavone is found naturally as the glycoside genistin and as the glycosides 6"-O-malonylgenistin and 6"-O-acetylgenistin.

Genistin and its glycosides are mainly found in legumes, such as soybeans and chickpears.

Genistein has weak estrogenic and antioxidant activities. It may also have anticarcinogenic, anti-atherogenic and anti-osteoporotic activities.

Genistein's weak estrogenic effect may help protect against osteoporosis by preventing bone resorption and promoting increased bone density.

There is a growing body of in vitro and animal studies suggesting that genistein may be helpful in preventing and treating some cancers, principally breast and prostate cancers.

A number of studies have shown that genistein can inhibit prostate cancer-cell growth in vitro. Some recent in vitro studies suggest that genistein may be both chemopreventive and therapeutic in prostate cancers regardless of androgen responsiveness. Clinical trials are needed.

Genistein is contraindicated in those who are hypersensitive to any component of a genistin, or genistein-containing product.