Drug Interactions Corner

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Contraceptive Failure Possible with St. John’s Wort


Because of a possible drug interaction, women on oral contraceptives should use additional nonhormonal contraceptives when they are taking St. John’s wort, especially if they experience breakthrough bleeding.


Lexi-Interacts monograph on oral contraceptives (estrogens)/St. John’s wort. Hudson, Ohio: Lexi-Comp; 2004.

Yue QY et al. Safety of St John’s wort [letter]. Lancet. 2000;355:576–7.

Hall SD et al. The interaction between St John's wort and an oral contraceptive. Clin Pharmacol Ther. 2003;74:525–35.

Pfrunder A et al. Interaction of St John's wort with low-dose oral contraceptive therapy: a randomized controlled trial. Br J Clin Pharmacol. 2003;56:683–90.