Brief: Do soy isoflavones help hot flashes?

What are soy isoflavones?

Isoflavones are plant compounds shaped a bit like the hormone estrogen². Soy is the most widely used food that contains them³. They're also sold as supplements, and red clover is another source^{2, 5}.

What did the studies find?

The 2013 Cochrane review included randomized trials of at least 12 weeks in women in perimenopause or after menopause who had hot flashes or night sweats. It tested soy foods, soy extracts, red clover extracts, genistein extracts and other plant estrogens¹.

Most trials couldn't be pooled. They were too different from each other. In the five red clover trials that could be combined, the difference from placebo in daily hot flashes wasn't significant¹.
Some trials found a benefit. Some soy and other plant-estrogen trials found fewer or milder hot flashes and night sweats than on placebo. But many were small, and the reviewers judged many at high risk of bias¹. Four trials of extracts high in genistein, one type of plant estrogen, consistently reduced how often hot flashes happened, and the reviewers said these deserve more study¹.
Placebo was powerful. In most trials, hot flashes on placebo fell by anywhere from 1% to 59%¹. That makes a small real effect hard to see.

The Menopause Society's 2023 review of newer soy trials found the same muddle. The trials tested very different products, many were small, and most measured results after about 12 weeks, though analyses suggest more than 16 weeks may be needed for the best effect³. It also notes that only about 35% of North American women can turn a soy isoflavone called daidzein into equol, which may be key to soy's estrogen-like effects. Tests to tell which women can do this aren't commercially available³.

What do the experts say?

The Menopause Society (2023): "Given mixed evidence of benefit for VMS, soy foods, soy extracts, and the soy metabolite equol are not recommended." (VMS means hot flashes and night sweats.) It rates this Level II, meaning limited or inconsistent evidence³.
ACOG (Clinical Practice Guideline No. 13, October 2026): "The available evidence does not support the efficacy or safety of phytoestrogens (eg, soy isoflavones) or herbal supplements for the treatment of vasomotor or other menopausal symptoms." It says the trials were small and tested very different products, doses and treatment lengths, and that these supplements aren't regulated by the FDA and haven't been tested for safety, effectiveness or purity. This is a statement in the guideline's text, not one of its graded recommendations⁴.
NIH's complementary health center (NCCIH) says soy isoflavone supplements or soy protein "may help to reduce the frequency and severity of menopausal hot flashes, but the effect may be small, and research results have not been completely consistent"².

Is soy safe?

Soy foods include tofu, miso, tempeh, edamame and soy milk². For supplements, NCCIH says soy protein has been used safely in studies for up to 16 weeks, and concentrated isoflavone extracts for up to 6 months². Side effects can include bloating, constipation, diarrhea and nausea, and some people are allergic to soy². In the Cochrane trials, plant-estrogen treatments used for up to two years showed no signs of stimulating the uterine lining or the vagina¹. Long-term safety hasn't been established, though, and because these supplements may act like estrogen, NCCIH says they may not be safe for women who shouldn't take estrogen⁵. The Cochrane review left out women with breast cancer or a history of it¹.

NCCIH advises anyone who takes medicine to talk with a health care provider before using soy or other herbal products². In the US, supplements aren't approved by the FDA before they're sold^{2, 6}.

The limitation

The Cochrane review searched for trials up to July 2013, and most of its trials were too different to combine¹. Newer trials tested very different products in widely varying amounts, so one product's result may not carry over to another bottle³. "Not shown to work" isn't the same as proven useless. It means the trials so far haven't shown a clear benefit.

One thing to try, one thing to ask

If you take a soy or red clover supplement, add it to the medicine list you bring to appointments. Several trials counted hot flashes per day¹, so a 2-week tally on our printable tracker gives you and your clinician something concrete. Then ask: "Soy had mixed results in trials. Is it safe for me, given my history, and which options with stronger evidence fit me?" Our hot flashes path lays out the options and how the evidence grades them.