The oestrogenic potency of the isoflavones has been well documented. Overgrazing cattle or sheep on red clover can be detrimental to their fertility. In ‘clover disease’, ewes are made permanently infertile by clover consumption. In animals with clover disease, the uterine response to oestrogen is reduced, as is the surge in LH. Clover disease has not been observed with normal therapeutic doses in humans. None of the trials has reported adverse effects. An isoflavone preparation from soya bean, and red clover extracts containing genistein, daidzein, biochanin A and formononetin, did not modify the endometrial architecture in 25 postmenopausal women taking the preparation for 1 year.
Controlled studies are not available; therefore, interactions are based on evidence of activity and are largely theoretical and speculative.
Red clover contains coumarin, which could theoretically exert anticoagulant activity and therefore increase the clinical effects of warfarin. However, it is only the byproduct, dicoumarol (produced by microorganism in poorly dried sweet clover) that has established anticoagulant effects. Interaction with anticoagulant medication is not likely for extracts from properly dried red clover. Observe patients taking red clover and anticoagulants concurrently.
Theoretically, if taken in large quantities, phyto-oestrogens may compete with synthetic oestrogens for receptor binding, but the clinical significance of this remains unknown. A recent review concluded that up to 2 mg of red clover-derived isoflavones per kg should be considered a safe dose for most patient groups.
Contraindications and Precautions
There are no known contraindications for the flower head extracts. Concentrated isoflavone extracts should only be used by people with oestrogen-sensitive cancers under professional supervision because of the possible proliferative effects. Additionally, people with conditions that may be aggravated by increased oestrogen levels, such as endometriosis or uterine fibroids, should use this herb under professional supervision only.
Scientific evidence for the use of red clover during pregnancy has not been established. No teratogenicity data are available. Use is not recommended.