Answers to Frequently Asked Questions About...
How to Use Emergency Contraception
What if I take the second dose of emergency contraceptive pills late?
The instructions for Next Choice, Levonorgestrel Tablets and some other progestin-only emergency contraceptive pills say that you should take two doses 12 hours apart (that’s one pill followed 12 hours later by another pill.) However, research shows that progestin-only emergency contraceptive pills (also called "morning after pills" or "day after pills") are equally effective if you take the two doses at the same time, take them 12 hours apart as recommended, or wait as long as 24 hours to take the second dose. That’s why, in many countries, the instructions for specially packaged progestin-only emergency contraceptive pills (like Postinor or NorLevo) say to take both pills at once.
Plan B One-Step and Next Choice One Dose are a single pill that contains the same amount of hormones found in two Next Choice or Levonorgestrel pills; if you're using Plan B One-Step or Next Choice One Dose, you simply take the pill as soon as possible after sex. Similarly, ella (ulipristal acetate) is just one pill that you take as soon as possible after sex (in clinical studies, the effectiveness of ella doesn't decline over a 5-day period, but for each individual woman, what's important is where she is in her own cycle; emergency contraceptive pills don't appear to work after ovulation has occurred).
Research about “combined” emergency contraceptive pills (those are pills containing both estrogen and progestin, such as regular birth control pills used in different doses as EC), in contrast, has focused on taking the two doses 12 hours apart. Even so, taking the second dose a little early or a little late (like a difference of two hours) will probably not make a difference in how effective the pills are.
A thorough and up-to-date academic review of research about how and when to take emergency contraceptive pills, as well as other medical and social science literature about emergency contraception is available here .