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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.

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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.

How to take it

TimingTiming does not matter.
With food?With food.
Worth knowingGround flaxseed also gives you fibre and ALA that an isolated lignan capsule does not, at a fraction of the price.

Interactions

With medications

  • tamoxifen and aromatase inhibitors

    Lignans are phytoestrogenic and their effect alongside endocrine therapy is not established. talk to your oncologist before starting

  • any oral medication, when taken as whole ground flaxseed

    The fibre slows and reduces absorption of drugs taken at the same time. separate by at least 2 hours

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Do flax lignans help hot flashes?

No: a phase III randomized placebo-controlled trial found flaxseed was no better than placebo for hot flashes, and an earlier trial reached the same conclusion. It is one of the clearer negative results among menopause supplements.

Do flax lignans lower breast cancer risk?

A systematic review found mostly observational and small mechanistic data suggesting possible favourable effects of flax on hormone metabolism, without trial evidence of clinical benefit. The evidence for flax lignans is limited.

How much flax lignan (SDG) should I take?

Trials of isolated SDG used roughly 50-100 mg daily, while retail lignan extracts commonly supply 20-50 mg per serving. Ground flaxseed also gives you fibre and ALA that a lignan capsule does not, at a fraction of the price.

Can I take flax lignans with tamoxifen?

Talk to your oncologist first: flax lignans are phytoestrogenic and their effect alongside tamoxifen or aromatase inhibitors is not established. Whole ground flaxseed also slows absorption of oral medication, so separate it by at least 2 hours.

Scientific references

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