Because of the estrogen-like properties in red clover isoflavones, women with a history of breast cancer should avoid red clover (some studies suggest that synthetic and/or natural estrogens may increase the risk of breast cancer). Red clover isoflavones 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.