Laboratory and animal studies have found that red clover isoflavones (a phytoestrogen) may protect against the growth of breast cancer cells. This is surprising because estrogens have generally been thought to stimulate the growth of breast cancer in women. Until further research has been conducted and more information is available, the use of red clover isoflavones or other red clover products should probably be avoided in women with a history of breast cancer.

Red clover isoflavones (phytoestrogen) should be used with caution, if at all, by people receiving hormone therapy (including birth control pills) containing estrogen, progesterone, androgen or any derivatives of these hormones. Because of the increased risk of bleeding associated with red clover, individuals taking blood-thinning medications (such as warfarin or aspirin) or blood-thinning herbs and supplements (such as ginkgo, ginger, garlic, and vitamin E) should avoid red clover.

Dried, unfermented red clover has no other known side effects in humans if used properly. However, infertility has been noted in grazing animals that consume large amounts of red clover. But, until no long-term study has been proved the safety of red clover, it should be taken carefully and for a short term only.

Tip:
Red clover has a history of short-term use as a cough remedy for children. Isolated red clover isoflavone products are very different than the whole herb, however, and are not recommended for children. Also the use of red clover is not recommended for pregnant or breastfeeding women.