Red clover is one of the most widely sold plant extracts for menopause, and one of the better tolerated. That is the short version, and it is true. The longer version matters more if you are on medication, have had a hormone-sensitive cancer, or are about to have surgery. This article sets out what the trials found, the handful of case reports that get quoted, and a plain list of who should talk to a doctor first. We sell a supplement that contains red clover, so read it knowing that, and check the references.
What the safety trials show
The longest controlled study of red clover isoflavones ran for three years. Researchers at the Royal Marsden gave 401 women with a family history of breast cancer either 40 mg of isoflavones a day or a placebo, and measured what mattered most in that group: breast density on mammograms, thickness of the womb lining, and hormone levels. After three years there was no difference between the groups on any of those measures, and no difference in the rate of breast cancer. The dose is the same 40 mg a day that most clinical trials used, and the same amount in EQUILI.
A separate one-year trial reached the same conclusion on breast density, which is worth stating because conventional HRT does increase it. And the Cochrane review that pooled the red clover trials found no sign of estrogen-like stimulation of the womb lining or vaginal tissue over up to two years of use.
So the evidence that red clover behaves like a weak plant compound rather than like a hormone is reasonably good. It is not evidence that it is safe for everyone, and the exceptions are specific.
Side effects reported in trials
Uncommon and mild. Across the placebo-controlled trials, the things reported more often with red clover than placebo were headache, nausea, and occasional spotting or a longer period in women still menstruating. Skin irritation has been reported. None of the trials found a serious adverse event they could attribute to the extract, and dropout rates for side effects were similar in the red clover and placebo groups.
Two individual case reports are quoted on almost every website about red clover, so here they are with their context. A 53-year-old woman had a subarachnoid hemorrhage, a type of stroke, while taking a product containing 250 mg of red clover and eight other herbs. The authors could not link it to red clover specifically. A 52-year-old woman had severe stomach pain and vomiting after three days on 430 mg of red clover while taking methotrexate for psoriasis, and recovered fully when she stopped. That one is more plausible, because both affect the liver, and it is why methotrexate is on the list below. Two case reports in twenty years of wide use is a reassuring number, not an alarming one, but they tell you where to be careful.
Who should not take it
- Pregnant, trying to conceive, or breastfeeding. There is no safety data at all, and red clover has mild estrogenic activity. Not a gray area.
- Under 18. Same reason.
Who should ask a doctor or pharmacist first
Anyone with a hormone-sensitive condition
Breast, ovarian or endometrial cancer, now or in the past. Endometriosis. Fibroids. The three-year trial above is reassuring for women with a family history, but it did not include women who had themselves had cancer, and no trial has. Isoflavones bind to estrogen receptors, weakly, and the honest position is that nobody has proven that is harmless in someone whose tumor responded to estrogen. Most oncologists say avoid it. Some say it’s fine. Ask yours.
Anyone on tamoxifen, aromatase inhibitors, HRT or the contraceptive pill
These all act on the same receptors or the same hormones. A 2020 study of 88 women taking tamoxifen found no interaction or serious side effects from red clover, which is encouraging, but it is one study and the drug is doing an important job. The same caution applies to HRT: there are no trials of the two combined, and taking two things that act on estrogen receptors without medical advice is not sensible.
Anyone on blood thinners, or with a bleeding disorder
Red clover contains small amounts of coumarins, the family of compounds warfarin was developed from, and it may slow clotting. That means warfarin, aspirin, clopidogrel and the newer anticoagulants. It also means stopping red clover at least two weeks before planned surgery and telling the anesthesiologist about every supplement you take. This is the interaction that pharmacists flag most.
Anyone on methotrexate
Because of the case report above. Methotrexate is used for rheumatoid arthritis and psoriasis as well as in cancer treatment, so this catches more people than it sounds.
Anyone with liver disease
Isoflavones are metabolized in the liver. If your liver is already under strain, or you take medicines that are, your doctor should know what else you are adding.
Anyone on regular medication of any kind
Interaction data for herbal extracts is thin, because nobody funds those studies. Absence of a reported interaction is not evidence of safety. A two-minute conversation with a pharmacist costs nothing.
The soy question
People often ask whether red clover carries the same concerns as soy. Both contain isoflavones. Red clover’s are mostly biochanin A and formononetin, which your gut bacteria convert into the genistein and daidzein found in soy, so the end products overlap. The safety evidence for the two is broadly similar, and if you have been told to avoid soy isoflavones for a medical reason, treat red clover the same way. If the reason was an allergy, red clover is a different plant and is not a soy allergen, but check the rest of the product’s ingredients.
How much is too much
The trials used 40 to 80 mg of isoflavones a day, and the three-year safety study used 40 mg. Products vary enormously, which is why we think the isoflavone content should be on the label in milligrams rather than as “red clover extract 500 mg”, which tells you nothing. Red clover tea is not the same thing: a cup contains an unknown and usually small amount of isoflavones, and the reports of side effects with tea involved people drinking well over a liter a day. Take what the label says, and don’t stack products that each contain isoflavones.
What to do if something feels wrong
Stop taking it. Headache, nausea or spotting that appears within days of starting and disappears when you stop is almost certainly the supplement, and you have your answer. Anything more than that, or anything that doesn’t settle, see a doctor and tell them what you were taking. Bring the bottle.
Where EQUILI stands
EQUILI provides 40 mg of red clover isoflavones a day, the dose from the three-year safety study, alongside sage, horsetail and flaxseed lignans. Every warning on this page is repeated on the product page and the label, and the full evidence is on our red clover review. If you are in one of the groups above, we would rather you asked your doctor and didn’t buy than bought and wondered.
References
- Powles TJ, et al. Red clover isoflavones are safe and well tolerated in women with a family history of breast cancer. Menopause International. 2008. PubMed 18380954
- Atkinson C, et al. Red-clover-derived isoflavones and mammographic breast density: a double-blind, randomized, placebo-controlled trial. Breast Cancer Research. 2004. PMC400670
- Lethaby A, et al. Phytestrogens for menopausal vasomotor symptoms. Cochrane Database of Systematic Reviews. 2013. PubMed 24323914
- Subarachnoid hemorrhage case report in a woman taking a multi-herb product containing red clover. 2007. PubMed 17634840
- Case report of a suspected red clover and methotrexate interaction. 2013. PubMed 24072635
- Study of red clover in 88 women taking tamoxifen. 2020. PubMed 31975316
- National Center for Complementary and Integrative Health. Red Clover. nccih.nih.gov
This article is for general information and is not a substitute for medical advice. Red clover is a food supplement ingredient, not a medicine. If you take any medication or have a medical condition, consult a doctor or pharmacist before use.