Will the medications I take make emergency contraceptive pills less effective?

Some enzyme inducer medications and herbal supplements, including a type of antibiotics used to treat tuberculosis; efavirenz, an antiviral used to treat HIV; St. John’s Wort; the seizure medication phenytoin (Dilantin); and the antifungal, griseofulvin, may reduce the effectiveness of emergency contraceptive (EC) pills. So if you are using an enzyme inducer, talk to a health care provider about if EC pills will be effective for you or consider getting an IUD for EC—it’s the most effective option regardless of your other medications.