Soy Isoflavones

Soy isoflavone · Soy isoflavone extract

Snapshot

Indications	Contraindications
Menopausal symptoms¹ Lumbar spine bone density² Systolic blood pressure^{3, 4} Cognitive function^{5, 6}	Breast cancer history or risk⁷ Soy allergy⁸ Pregnancy or lactation⁹

Soy isoflavones, chiefly genistein, daidzein, and glycitein, are plant compounds structurally similar to estrogen, sold as supplements alongside soy protein¹⁰. They act as selective estrogen receptor modulators rather than as estrogen itself¹¹. That receptor activity underlies their use in postmenopausal women for menopausal symptoms, bone density, and blood pressure, and for arterial stiffness and cognition, where trials are more variable.

Extract supplements raised lumbar spine bone density in a meta-analysis, but a two-year trial found they did not prevent decline. In postmenopausal women, a 2025 randomized pilot trial found skin improvements with an isoflavone extract tracked with gut-derived equol production in exploratory analysis, though the primary wrinkle outcome was not significant¹². Products listing soy isoflavones are mostly capsules and tablets, often combined with other menopause ingredients; see Form comparison.

Health Canada lists breast cancer history or predisposition as a contraindication on licensed labels⁷, and animal data show genistein can blunt tamoxifen⁸. Memorial Sloan Kettering asks patients taking tamoxifen or aromatase inhibitors to talk with their healthcare provider⁸.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

73 sources, 57 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources