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The Emergency Contraception Website - Your website for the "Morning After"

Answers to Frequently Asked Questions About…


How effective is emergency contraception?

Emergency contraception (also known as "morning after pills" or "day after pills") makes it much less likely that you will get pregnant if taken within the first few days after you have sex. How much it reduces your chances of getting pregnant depends on which kind of emergency contraceptive you use and how quickly you take it after unprotected intercourse. In general, progestin-only emergency contraceptive pills, like Plan B One-Step, Next Choice One DoseTake Action  and Levonorgestrel Tablets, are more effective than combined emergency contraceptive pills. And pills containing an antiprogestin, like ella, are more effective than progestin-only pills.

Labeling for Plan B One-Step, Next Choice One Dose, Next Choice and Levonorgestrel Tablets states that the treatment prevents 7 of 8 pregnancies that otherwise would have occurred; that means it reduces your risk of pregnancy by 88%*. And if you take these progestin-only emergency contraceptive pills within the first 24 hours after sex, they reduce your risk of pregnancy by up to 95%.


The risk of pregnancy after taking ella within 24 hours after sex is about 65% lower than the risk after taking progestin-only pills such as Plan B One-Step, Next Choice One Dose, Next Choice or Levonorgestrel Tablets; if taken within 72 hours after sex, the risk is 42% lower. In clinical studies, ella stayed effective for 5 days after unprotected sex; but what matters for each individual woman is where she is in her own cycle (if a woman is about to ovulate, she may risk pregnancy if she waits 5 days to take EC). Although ella works closer to the time of ovulation than progestin-only EC (such as Plan B One-Step), emergency contraceptive pills – including ella – do not appear to work if you are too close to ovulation, or have already ovulated. You may not know exactly how close you are to ovulating; so take EC as soon as possible after unprotected sex, no matter which pill you use.


Emergency contraceptive pills containing both progestin and estrogen (known as “combined” pills) reduce the risk of pregnancy by 75%. In other words, if 100 women use this type of pill after having unprotected sex, only 2 of them will get pregnant. Emergency insertion of a copper-T IUD reduces the risk of pregnancy by more than 99%.


While all of these types of emergency contraceptives are safe and effective, with the exception of the IUD (if used for ongoing contraception), they are not as good at preventing pregnancy as birth control that’s used before or during sex, like the pill or condom. If emergency contraception was the only type of birth control you used for an entire year, your annual risk of getting pregnant would probably be about 20% with progestin-only EC such as Plan B One-Step, Next Choice One Dose, Next Choice, Levonorgestrel Tablets and other progestin-only emergency contraceptive pills and 40% with “combined” emergency contraceptive pills. And that’s assuming you used emergency contraceptive pills perfectly, after each and every time you had unprotected sex. For this reason, health care providers generally recommend that, if you are sexually active, you should try to find a regular method of contraception other than emergency contraception that can work for you. (Find out more about your options here or use this free, interactive online tool or ARHP’s Method Match to help choose the best contraceptive method for you.)

* The exact effectiveness of emergency contraceptive pills is difficult to measure and some researchers believe the effectiveness may be lower than that reported on package labels. To find out more about studies evaluating the effectiveness of emergency contraception, read our thorough and up-to-date academic review of the medical and social science literature here.




This website is operated by the Office of Population Research at Princeton University and has no connection with any pharmaceutical company or for-profit organization.

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