John's wort along with birth control pills might decrease the effectiveness of birth control pills. If you take birth control pills along with St. John's wort, use an additional form of birth control such as a condom.

How much does St John's wort affect birth control?

Results: Treatment with St. John's Wort was associated with a significant 13-15% reduction in the dose exposure from the contraceptive.

Does St John's wort affect contraceptive pill?

How does it affect the contraceptive pill? St John's Wort treatment contains an enzyme called cytochrome P40 which increases the rate of metabolism of the pill. This reduces the effectiveness of the pill by causing a reduced concentration of the contraceptive in the body.