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Is EC less effective if you are using an enzyme inducer (such as Dilantin, rifampicin, griseofulvin, or St. John’s Wort)?

Medications and herbal supplements that may make regular contraceptive pills less effective may also reduce the effectiveness of EC pills. So if you are using an enzyme inducer, it probably makes sense to increase the dose of EC. You should talk to your provider about how much to increase the dose.


  1. World Health Organization Department of Reproductive Health and Research and Johns Hopkins Bloomberg School of Public Health Center for Communication Programs (2018) Family Planning: A Global Handbook for Providers. Baltimore and Geneva. Retrieved from https://apps.who.int/iris/bitstream/handle/10665/260156/9780999203705-eng.pdf?sequence=1

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