Soy Isoflavone Supplements for Hot Flashes: How Much Do They Help?

Soy contains isoflavones, plant compounds with a structure similar to estrogen.¹ That’s why soy isoflavone pills are marketed for hot flashes. Here is what the research shows.

What the trials found

A 2012 review combined 19 randomized, placebo-controlled trials. Women took soy isoflavones (a median of 54 mg a day) for 6 weeks to a year. Compared with placebo:²

• Hot flash frequency dropped about 21% more.
• Severity dropped about 26% more.
• Supplements with more than about 19 mg of genistein, one type of isoflavone, were more than twice as effective at cutting frequency.

Results varied widely between studies.² An earlier review found the trials so different and flawed that it could only call the evidence an indication, not proof.³ The National Center for Complementary and Integrative Health (NCCIH)¹ sums it up: soy may reduce hot flash frequency and severity, but the effect may be small and results haven’t been consistent.¹

Other possible effects

NCCIH says soy isoflavones probably help bone density after menopause, and may modestly lower blood pressure. Soy supplements haven’t been shown to reduce breast cancer risk.¹

Safety

• Concentrated isoflavone extracts have been used safely in studies for up to 6 months.¹
• Side effects can include bloating, constipation, diarrhea and nausea.¹
• Some soy foods high in tyramine, such as tofu and soy sauce, can interact dangerously with MAOI antidepressants.¹
• Some people are allergic to soy.¹
• Supplements don’t need FDA approval before sale.¹

If you’ve had breast cancer or another hormone-sensitive condition, ask your oncologist before trying any supplement with estrogen-like compounds.

Before you buy

1. Check the label for total isoflavones and genistein content per dose.²
2. Consider soy foods such as tofu, edamame or soy milk as part of your diet.¹
3. Give it a fair trial, about 12 weeks, and track your hot flashes.
4. Avoid combination blends so you know what’s working. Our guide to menopause supplement blends explains why.

Our articles on black cohosh and hot flash help without hormones compare other options.

Try: “I’d like to try soy isoflavones for my hot flashes before considering hormones. Is that safe with my health history, and how long should I try it?”

My Body Changed. Now What? includes a Visit Brief. Use it to track your hot flashes before and after starting a supplement, and bring it to your appointment. See the book.