The purpose of this study is to evaluate the effects of a common herbal remedy, St. John's Wort, on the effectiveness of birth control pills. St. John's Wort has recently been shown to increase metabolism of some drugs. If it could increase metabolism of oral contraceptives as well, it may increase the risk of contraceptive failure and unintended pregnancy. Study participants will be evaluated for risk of ovulation on oral contraceptives before and during simultaneous therapy with St. John's Wort.

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Inclusion Criteria:

• Women taking or willing to take low dose oral contraceptives for 5 months
• No contraindications to hormonal contraception