Genistein

PhytochemicalIsoflavone

What is it

Genistein is a soy isoflavone (phytoestrogen) with weak estrogenic and anti-estrogenic effects. It is found in soybeans and other legumes and is the most studied isoflavone for menopausal symptoms and bone health.

Evidence for 2 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Menopausal hot flashes

Good Evidence

Multiple trials suggest genistein and soy isoflavones modestly reduce hot flash frequency and severity, though effects are smaller than hormone replacement therapy.

Bone health (postmenopausal)

Good Evidence

Some trials show modest benefits on bone density markers with genistein supplementation, especially in early postmenopause.

How it works

Genistein binds to estrogen receptors (with relative preference for ER-beta over ER-alpha), producing weak estrogenic effects in some tissues and antagonist effects in others. It is also a tyrosine kinase inhibitor and antioxidant. Clinical evidence supports modest benefits for menopausal hot flashes and possibly bone density preservation. Effects on breast cancer risk are debated, with epidemiological data from Asian populations suggesting possible protective effects from soy isoflavone intake during early life.

Dosage

Studies for menopausal symptoms typically use 40-80 mg of genistein per day. Soy food intake delivers about 30-50 mg of total isoflavones per cup of soy milk or 100 g of tofu.

When and how to take it

WHEN: Once or twice daily, with consistency over weeks/months matters. HOW: With water; food may help absorption.

2 commercial forms

Compare the main delivery options and what they’re best suited for.

Pure genistein

Standardized isolated isoflavone.

Less common in supplements than mixed soy isoflavones.

Soy isoflavone complex

More common supplement form; closer to dietary soy.

Contains genistein, daidzein, and glycitein.

Safety

Generally well tolerated. Side effects include mild GI upset and possible breast tenderness. Long-term high-dose safety in hormone-sensitive conditions is debated.

Who should be cautious

Discuss with clinician if you have a history of estrogen-sensitive cancer (breast, uterine) or are on tamoxifen. Caution with thyroid disorders and at supplement doses during pregnancy or breastfeeding.

Interactions

May interact with tamoxifen, aromatase inhibitors, and other hormone-modulating drugs. May affect thyroid medication absorption (separate by 4 hours). Possible interaction with anticoagulants at high doses.

Food sources

Soybeans, tofu, tempeh, miso

Amount
1/2 cup
%DV
—

Frequently asked questions

Is soy isoflavone safe for women with breast cancer history?⌄

This is debated. Some research suggests dietary soy intake is safe or beneficial; high-dose isoflavone supplements are more controversial. Discuss with your oncologist.

Will genistein cause hormonal side effects in men?⌄

At supplement doses, soy isoflavones do not consistently affect testosterone in men. Effects are weak compared to actual hormones.

References

Genistein on Wikidata — Wikidata link

Genistein (ChEBI:28088) — ChEBI link

Genistein (PubChem CID 5280961) — PubChem link

Genistein on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Genistein (PubMed search) — PubMed link

Track Genistein with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.