When eaten in normal, moderate amounts, foods are unlikely to interact with prescription birth control pills. No peer-reviewed scientific evidence supports the notion that any food will prevent oral contraceptives from functioning properly; nevertheless, many women are concerned that hormone-affecting foods may cause unplanned pregnancy. Several common foods, including licorice, yam, soy and dairy products, can theoretically impair the effectiveness oral contraceptives.
Natural licorice is potently medicinal; women taking birth control pills should eat it only in moderation. Not only can licorice raise blood pressure levels--a common side effect also associated with oral contraceptives--but it can also have unanticipated effects on reproductive hormones. In theory, large quantities of licorice could result in an unplanned pregnancy.
In naturopathy, soy is often used as a holistic treatment for hormone imbalances caused by menopause and polycystic ovarian syndrome. Soybeans contain natural hormone-like compounds that imitate the role of estrogen in the human body. The National Institutes of Health warn that these hormonal effects could, in theory, interact with birth control.
For several generations, wild yam has been used in herbal blends and estrogen creams to increase progesterone levels. According the National Institutes of Health, scientific evidence has disproven the theory that wild yam can improve fertility; nevertheless, NIH cautions against the use of wild yam in women taking oral contraceptives.
In the United States, some dairy companies use milk from cattle treated with recombinant bovine growth hormone (RBGH), a controversial compound used to increase a cow's milk output. In theory, large amounts of RBGH-treated milk could interact with birth control pills; women taking oral contraceptives may choose to avoid dairy products from RBGH-treated cattle.