Does St. John’s wort interact with hormonal birth control methods?
Data are sparse. In 2005, Murphy et. al. gave a group of women low-dose oral contraceptive pills (OCPs) and St. John’s wort supplements. Women who took both medications were significantly more likely to experience breakthrough bleeding than OCP users who did not use St. John’s wort. Additionally, there was an increased rate of follicles over 30 mm in diameter among women who took both medications, possibly indicating ovulation while taking the pill. Studies by Hall et. al. (2003) and Pfrunder et. al. (2003) also found higher incidences of breakthrough bleeding in women taking both medications, but did not confirm the increase in follicle size or evidence of ovulation. All three studies showed that St. John’s wort increases the clearance of norethindrone and lowers the half-life of ethinyl estradiol, but did not demonstrate a reduction in efficacy of the birth control or an increase in the risk of unintended pregnancy.
Without the benefit of larger studies, we don’t know whether St. John’s wort lowers the efficacy of oral contraceptives. Women who take St. John’s wort should consider using a barrier method along with oral contraceptive pills. Pill users who need medication for depression should consider something other than St. John’s wort. The possible interaction between St. John’s wort and oral contraceptives highlights the importance of asking patients about their use of health supplements.
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Murphy PA, Kern SE, Stanczyk FZ, & Westhoff CL. Interaction of St. John’s Wort with oral contraceptions: Effects on the pharmacokinetics of norethindrone and ethinyl estradiol, ovarian activity and breakthrough bleeding. Contraception. 2005;71(6), 402-408.
Pfrunder A, Schiesser M, Gerber S, et al. Interaction of St. John’s wort with low dose oral contraceptive therapy: A randomized controlled trial. British Journal of Clinical Pharmacology. 2003; 56: 683-90.
The Reproductive Health Access Project does not accept funding from pharmaceutical companies. We do not promote specific brands of medication or contraception. The information in the Contraceptive Pearls is unbiased, based on science alone.