The effectiveness of oral contraceptives can be weakened by the use of certain medicinal herbs. Because most plant-based medicines are pharmacologically complex, unanticipated interactions between herbs and allopathic drugs are common. Most interactions between birth control pills and herbs have been unreported by peer-reviewed literature, so medical understanding is limited. To prevent unintended pregnancy, women taking birth oral contraceptives should avoid the following herbs unless they are using another contraceptive technique.
St. John's Wort
The popular herbal antidepressant, St. John's Wort, is contraindicated for women using oral contraceptives. It interferes with the absorption of many medicinal compounds, so most physicians and herbalists advise against its use for people taking prescription drugs. According to the National Institutes of Health, St. John's Wort can contribute to altered menstrual cycles and unintended pregnancy for women taking oral contraceptives. Additionally, women taking St. John's Wort with birth control pills have reported heavier periods and severe cramping.
Vitex, also known as chasteberry or chaste tree berry, is frequently used by women who are experiencing infertility and menstrual disorders. While vitex is a popular and effective treatment for pre-menstrual syndrome, it should not be used by women who rely exclusively on oral contraceptives for birth control. Vitex is believed to induce ovulation and strengthen the lining of the uterus-- in essence, it reverses the contraceptive process created by birth control pills. Most herbalists advise women to avoid chasteberry unless they are actively trying to conceive.
Most commonly used for the treatment of hot flashes and other menopausal disorders, black cohosh is believed to contain significant levels of phytoestrogens. These plant-based compounds are similar to estrogen and may interact unpredictably with birth control pills and other hormone-affecting compounds. Black cohosh is also a known emmenogogue and anticoagulant, so it can cause heavy, painful periods and between-cycle bleeding. Because of its effects on hormone levels and menstrual cycles, black cohosh should be avoided by women using oral contraceptives.
Also known as Chinese angelica, dong quai produces many effects that are similar to black cohosh. Like black cohosh, it has mild estrogenic activity which may decrease the effectiveness of oral contraceptives. The National Institutes of Health warn that it also has anticoagulant effects, and it appears to have alter the the lining of the uterus. Additionally, dong quai can contribute to hypertension-- a common concern for women taking birth control pills. Research about dong quai is very limited, and experts are uncertain about whether it increases or decreases fertility. Until more is known, it should be avoided by women using oral contraceptives.
Soy is one of the most popular (and controversial) botanicals used in herbal medicine. Of the hormone-affecting plants, soy contains the highest concentration of estrogen-mimicking compounds. Foods containing soy usually provide too little phytoestrogen to have any noticeable effect on the efficacy of birth control pills. However, soy isoflavones (sold as dietary supplements) may drastically alter hormone levels in the body. This effect can produce irregular menstruation, dizziness, gastrointestinal problems and headaches for women taking oral contraceptives. They also could contribute to unintentional pregnancy by encouraging ovulation.