What are phytoestrogens?
Phytoestrogens are substances that certain plants produce and are chemically similar to the human hormone estrogen. Phytoestrogens, the plant-based estrogens, are several times less potent than normal human estrogen yet some scientific studies have shown beneficial effects. Phytoestrogens are available in several supplements. The most common include black cohosh, dong quai and soy.
Phytoestrogens have been used to treat the signs and changes of menopause, including hot flashes, vaginal dryness, dry skin, osteoporosis, depression, mood swings, fatigue, and sleep problems.
Medical research has not proven that phytoestrogens are effective in treating menopause or any medical condition. Nor have studies directly compared phytoestrogens with prescription therapy. Because phytoestrogens are less potent and their benefits are less clearly defined than prescription estrogens, they are not typically the first choice for hormone replacement therapy.
Potential drug interactions with phytoestrogen
Women taking birth control pills, estrogen therapy, azathioprine (Imuran®), cyclosporine (Sandimmune®, Neoral®), or blood pressure medicines should not take the phytoestrogen black cohosh. Dong quai may interact with anticoagulants (blood thinners) like warfarin (Coumadin®) and daily aspirin therapy.
Soy may prevent the thyroid medicine levothyroxine (Synthroid®) from being absorbed into the body. If you are taking levothyroxine and soy, it's best to separate your levothyroxine dose from any soy supplements by at least two hours. You should talk to your doctor if you are taking iron supplements or warfarin (Coumadin®). Concentrated phytoestrogen supplements may interfere with the use of tamoxifen (Nolvadex®), so please make sure you tell your doctor if you are taking this medication.