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.
Click here for more detailed
instructions for using ella, Plan B One-Step, Next Choice One Dose, Next Choice, Levonorgestrel Tablets, or
daily birth control pills for emergency contraception.
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 
.