Some antibiotics can interfere with the effectiveness of your birth control pills. How much of a decrease it causes is unknown. The concern is whether or not the effectiveness is lowered enough to allow a break through ovulation to occur. Taking the majority of the antibiotic during your placebo pills was probably helpful. It is good that you started a new pack on time, and that you take your pills consistently. Plan B would not be effective at this point.
If your next period is more than 1 week late, do a pregnancy test.
27. February 2012
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