Other common name(s): purple clover, trefoil, wild clover
Scientific/medical name(s): Trifolium pratense
Red clover is a perennial plant that grows wild in the Americas, Europe, Australia, Asia, and northern Africa. The flower head, which ranges from pink to purple or red, is the part of the plant used in herbal remedies.
Available clinical evidence does not show that red clover is effective in treating or preventing cancer, menopausal symptoms, or any other medical conditions. It may also increase the risk of excessive bleeding in some people. Some of its extracts (isoflavones) are being tested to determine whether they help symptoms of menopause or reduce the level of bad cholesterol in the blood. So far, results are mixed. Studies looking at the extracts’ effectiveness against prostate enlargement and prostate cancer have begun. Other researchers are looking at whether it will help blood pressure and insulin resistance in diabetics and osteoporosis in women. Early findings suggest it may merit further testing.
How is it promoted for use?
Proponents claim that red clover is useful for relieving menopausal symptoms because it contains chemicals that are similar to the hormone estrogen. They also claim that the herb suppresses coughs (particularly whooping cough) and slows blood clotting. According to some practitioners, people who take prescription blood-thinning medications, such as warfarin (Coumadin), may be able to reduce their dosage by taking red clover supplements.
Other supporters claim that red clover is effective for treating cancers of the breast, ovaries, and lymphatic system, although available scientific evidence does not support this. A few claim that the herb acts as an antibiotic, an appetite suppressant, and a relaxant. Some believe that red clover preparations can be used to help speed wound healing and ease chronic skin conditions such as psoriasis.
What does it involve?
Red clover supplements are available as tablets, capsules, or in liquid extract form. Dried red clover can be brewed into a tea. Practitioners generally use a daily dosage of about 4 grams of dried red clover, or 1.5 to 3.0 milliliters of liquid extract. (Five milliliters is equal to one teaspoon, so this would be around ¼ to ½ teaspoon of the liquid.) The liquid extract can be rubbed directly on skin or applied with a compress. Dried red clover can also be made into a tea and either drunk or used as a wash. It also comes in cream, lotion, or ointment form for use on the skin and is sometimes used in cosmetics and soaps.
What is the history behind it?
For centuries, red clover has been grown in pastures to feed cattle and other grazing animals. The herb is an ingredient in the Hoxsey formula, Jason Winters’ tea, and Essiac tea, which are common herbal remedies (see Hoxsey Herbal Treatment and Essiac).
What is the evidence?
Scientists have identified phytoestrogens (estrogen-like substances from plants) called isoflavones, mainly biochanin and formononetin, in red clover. These 2 are precursors of the isoflavones daidzein and genistein, which are found in smaller amounts in red clover and also in soy. Low levels of anti-coagulant, or blood-thinning, chemicals called coumarins are also present in red clover. These substances have been identified in the plant, however, most of the claims made for the herb have not been verified in humans through randomized clinical trials.
One group of Australian researchers gave red clover isoflavonoids to 20 men with prostate cancer before they had prostatectomies (surgery to remove the prostate). The men who had received flavonoids appeared to have more cancer cells that were dying in their surgically removed prostate tissue. This was a very small study, without a placebo group, and it did not compare survival, quality of life, or symptoms. How this might affect treatment is not yet known. Further studies are needed.
Most studies suggest that long-term use (10 years or more) of estrogen replacement therapy after menopause may increase the risk of heart disease and breast and endometrial cancers. Scientists are looking for estrogen alternatives that do not increase these risks, and phytoestrogens from red clover have been targeted for research.
In a small clinical study, researchers concluded that a diet supplemented with red clover sprouts and other plants that contain phytoestrogens may reduce the severity of menopausal symptoms. However, this needs to be confirmed in other studies before red clover can be routinely recommended. Studies of commercial red clover isoflavone supplements for relief of menopausal symptoms have shown conflicting results, although most (including the largest study) found no reduction of hot flashes and no improvement in relevant quality of life measures.
Several studies of isoflavone extracts from red clover have since shown mixed results on heart disease risk factors such as cholesterol and triglycerides. For example, in a 2005 study, sixty post-menopausal women taking red clover isoflavones had slightly lower triglyceride levels and fewer menopausal symptoms than those on placebo. No significant difference in LDL, or "bad," cholesterol was noted.
An Australian study looked at both men and women taking enriched red clover isoflavones. One supplement was enriched with the phytoestrogens formononetin and the other with biochanin. These were compared with placebo for six weeks. The men receiving the biochanin-enriched supplement had somewhat lower levels of LDL cholesterol, but the women did not.
Preliminary studies have looked at the use of isoflavones from red clover to control blood pressure in diabetic patients and to treat insulin resistance, osteoporosis, and benign prostatic hypertrophy (enlarged prostate). Most of these studies were small and did not last very long, and no conclusions can be reached about red clover isoflavones’ possible effectiveness for these conditions. Further studies are needed. It is also important to note that the extracts are not the same as the whole herb, and study results would not be likely to show the same effects.
Are there any possible problems or complications?
This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must provide the FDA with results of detailed testing showing their product is safe and effective before the drug is approved for sale), the companies that make supplements do not have to show evidence of safety or health benefits to the FDA before selling their products. Supplement products without any reliable scientific evidence of health benefits may still be sold as long as the companies selling them do not claim the supplements can prevent, treat, or cure any specific disease. Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). Though the FDA has written new rules to improve the quality of manufacturing processes for dietary supplements and the accurate listing of supplement ingredients, these rules do not take full effect until 2010. And, the new rules do not address the safety of supplement ingredients or their effects on health when proper manufacturing techniques are used.
Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.
Red clover is categorized as "generally recognized as safe" by the US Food and Drug Administration (FDA), and small amounts are included in some teas and "health drinks." Patients with bleeding problems or who take anticoagulant medications, including aspirin, may want to avoid red clover because of the slight chance it could increase the risk of serious bleeding. In addition, since the amount of the blood-thinning chemical coumarin in red clover varies, it cannot be relied on to produce the same effect even when the same dose is taken. Additional potential interactions between red clover and other drugs and herbs should be considered. Always tell your doctor and pharmacist about any herbs you are taking.
Women who have had estrogen receptor-positive cancers or who are pregnant or breastfeeding should not use this herb. No reports of toxicity or overdose from red clover were found in the available medical literature, although those who are allergic to clover should avoid it. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.
More information from your American Cancer Society
The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).
The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management
Bown D. New Encyclopedia of Herbs & Their Uses. New York, NY: DK Publishing Inc; 2001.
Fetrow CW, Avila JR. Professional's Handbook of Complementary & Alternative Medicines. Philadelphia, PA: Lippincott Williams & Wilkins; 2004.
Gruenwald J. PDR for Herbal Medicines. 3rd ed. Montvale, NJ: Thomson PDR; 2004.
Howes JB, Bray K, Lorenz L, Smerdely P, Howes LG. The effects of dietary supplementation with isoflavones from red clover on cognitive function in postmenopausal women. Climacteric. 2004;7:70-77.
Howes JB, Tran D, Brillante D, Howes LG. Effects of dietary supplementation with isoflavones from red clover on ambulatory blood pressure and endothelial function in postmenopausal type 2 diabetes. Diabetes Obes Metab. 2003;5:325-332.
Jarred RA, Keikha M, Dowling C, et al. Induction of apoptosis in low to moderate-grade human prostate carcinoma by red clover-derived dietary isoflavones. Cancer Epidemiol Biomarkers Prev. 2002;11:1689-1696.
Knight DC, Howes JB, Eden JA. The effect of Promensil, an isoflavone extract, on menopausal symptoms. Climacteric. 1999;2:79-84.
Nestel P, Cehun M, Chronopoulos A, et al. A biochanin-enriched isoflavone from red clover lowers LDL cholesterol in men. Eur J Clin Nutr. 2004;58:403-408.
Red clover. Drug Digest Web site. Accessed at www.drugdigest.org/DD/DVH/HerbsWho/0,3923,552774|Red%2BClover,00.html on June 6, 2008.
Red clover. Memorial Sloan-Kettering Cancer Center Web site. Accessed at www.mskcc.org/mskcc/html/69350.cfm on June 6, 2008.
Tice JA, Ettinger B, Ensrud K, et al. Phytoestrogen supplements for the treatment of hot flashes: the Isoflavone Clover Extract (ICE) Study: a randomized controlled trial.[see comment]. JAMA. 2003;290:207-214. Comment in: ACP J Club. 2004;140:47 and J Fam Pract. 2003;52:846-847.
US Food and Drug Administration. Department of Health and Human Services. Code of Federal Regulations, Food and Drugs (21), vol 3, Section 182. April 1, 2005.
van de Weijer PH, Barentsen R. Isoflavones from red clover (Promensil) significantly reduce menopausal hot flush symptoms compared with placebo. Maturitas. 2002;42:187-193.
Wilcox G, Wahlqvist ML, Burger HG, Medley G. Oestrogenic effects of plant foods in postmenopausal women. BMJ. 1990;301:905-906.
Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.
Last Revised: 11/28/2008