Limited evidenceWomen's health

Flax Lignans (SDG)

Concentrated secoisolariciresinol diglucoside from flaxseed, sold for hormone balance. The best-designed trials of flax for hot flashes were negative, and effects on hormone-related outcomes remain unproven.

Evidence last reviewed: August 2026

What the science says

Hot flashes Limited evidence
A phase III randomized placebo-controlled trial of flaxseed for hot flashes found no benefit over placebo, and an earlier randomized trial of a flaxseed-rich food reached the same conclusion. This is one of the clearer negative results in the menopause supplement literature.
Breast cancer and hormone markers Limited evidence
A systematic review of flax and breast cancer found mostly observational and small mechanistic data suggesting possible favorable effects on hormone metabolism, without trial evidence of clinical benefit.
Metabolic effects of isolated SDG Limited evidence
A placebo-controlled randomized crossover trial of an isolated flaxseed lignan supplement measured changes in circulating bile acids, an exploratory biochemical outcome rather than a health endpoint.

Dosage & safety

Studied doseTrials of isolated SDG have used roughly 50-100 mg daily; whole-flaxseed hot flash trials used about 40 g of ground flaxseed per day. Retail lignan extracts commonly supply 20-50 mg SDG per serving.

SafetyGenerally well tolerated; higher doses cause bloating and loose stools. Fibre content can slow absorption of medications taken at the same time. Its phytoestrogenic activity means women with hormone-sensitive cancers should discuss use with their oncologist.

Scientific references

A phase III, randomized, placebo-controlled, double-blind trial of flaxseed for the treatment of hot flashes: North Central Cancer Treatment Group N08C7
Pruthi S, Qin R, Terstreip SA, Liu H, Loprinzi CL, Shah TR — Menopause, 2012
Flax and Breast Cancer: A Systematic Review
Flower G, Fritz H, Balneaves LG, Verma S, Skidmore B, Fernandes R — Integr Cancer Ther, 2014
Effect of a Flaxseed Lignan Intervention on Circulating Bile Acids in a Placebo-Controlled Randomized, Crossover Trial
Navarro SL, Levy L, Curtis KR, Elkon I, Kahsai OJ, Ammar HS — Nutrients, 2020

Where to buy

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