Soy milk, a beverage derived from the soybean, is well-known for its nutritional profile and purported medicinal properties. According to the University of Maryland Medical Center, soy milk can reduce the risk of some forms of heart disease and cancer, and it may help improve health after menopause. Soy milk contains compounds similar to the human reproductive hormone estrogen, which is a key component of most birth control pills. However, soy milk is not known to alter the safety or efficacy of contraceptives.
Birth Control Function
Birth control pills, or oral contraceptives, generally contain a combination of estrogen and progesterone, two hormones involved in regulating the female reproductive system. The synthetic hormones in birth control pills prevent the body from ovulating, or releasing a viable egg. Contraceptives also make the womb less hospitable to sperm and newly fertilized eggs. In theory, any product containing estrogen, or estrogenic compounds, could augment the efficacy and side effects of hormone-based birth control products.
Hormonal Effects of Soy Milk
Soy beans contain trace amounts of estrogen-like compounds known as isoflavones. These compounds are not true hormones, but do appear to alter hormone levels when consumed in excessive quantities. The Sloan-Kettering Cancer Center acknowledges that soy isoflavones may influence estrogen levels, leading to increases in bone density and fewer symptoms of menopause. MayoClinic.com notes that dosages of between 10 and 106 grams of soy protein per day have been studied for their medicinal effects; these doses provide approximately between 30 and 100 milligrams of isoflavones each day.
Because large quantities of soy milk can influence the same hormones involved in contraception, soy milk could theoretically influence the safety, efficacy and potential side effects associated with birth control. Sloan-Kettering notes that excessive consumption of soy milk can cause hormone-related side effects, such as abnormal uterine bleeding, which are also seen among women taking birth control pills. Scientists have not specifically investigated the rate of side effects or unplanned pregnancy among women using contraceptives in conjunction with soy milk.
Despite theoretical concerns regarding the combination of contraceptives and soy milk, there is no specific evidence suggesting that normal dietary quantities of soy milk can interact negatively with birth control pills. MayoClinic.com does not advise birth control users to avoid soy milk. The University of Maryland advises that soy may adversely interact with the cancer drug tamoxifen and the osteoporosis treatment raloxifene.