Which herbal preparation is associated with reduced effectiveness of oral contraceptives?

• A. Ginseng
• B. Gingko biloba
• C. St. John's wort
• D. Saw palmetto

Answer: (C)

The main concept is that some herbs can speed up how the liver processes drugs, lowering their blood levels and effectiveness. Saint John’s wort is a strong inducer of hepatic enzymes, especially cytochrome P450 3A4, and it also boosts P-glycoprotein activity. This increases the metabolism and clearance of the hormonal components in oral contraceptives (ethinyl estradiol and progestin), which can reduce their circulating levels and undermine their ability to prevent ovulation. As a result, breakthrough bleeding can occur and the risk of pregnancy rises if Saint John’s wort is used with oral contraceptives. For this reason, it’s advised to avoid Saint John’s wort while using birth control pills or to use an additional nonhormonal method during co-use and for a period after stopping. The other herbs listed don’t have as clear or reliable a interaction with oral contraceptives in reducing their effectiveness.