Emergency contraceptive pills (ECPs), also known as “postcoital contraception” or the “morning-after pill,” work by changing a woman’s hormone levels in the same ways birth control pills and other hormonal methods work.
They give the body a short, high burst of synthetic hormones that disrupt natural hormone production needed for ovulation and pregnancy. ECPs prevent pregnancy by inhibiting ovulation or by disrupting egg and sperm transport, fertilization, or implantation. Most women can safely use ECPs even if they cannot use birth control pills as their regular method of birth control. ECPs can be used within five days of unprotected sexual intercourse.
It is not advisable to use ECPs as your only protection against pregnancy if you are sexually active or planning to be, because they are not as effective as other contraceptive methods.
The FDA currently approves three different types of emergency contraceptive pills: pills that contain only progestin, pills that contain both progestin and estrogen, and pills that contain the antiprogestin ulipristal acetate. (Mifepristone, or RU‑486, can also be used for emergency contraception. It has a lower pregnancy rate and fewer side effects than currently available pills 25 but has not been approved for this use in the United States.
Progestin-only ECPs include Plan B, Plan B One-Step, Next Choice, and the minipill. Progestin-only ECPs are slightly more effective than combination pills and cause few if any side effects.
The second type of ECP uses both estrogen and progestin. Currently, no combination pills are sold specifically as ECPs, but many brands of the daily birth control pill can be used at a higher dose for emergency contraception. To find out which pills you can use and the proper dose for each, visit the Emergency Contraception website or call the Emergency Contraception Hotline at 1-800-584-9911. This method often causes nausea and discomfort, but many women believe that the protection is worth it.
The newest ECP, the antiprogestin pill Ella, is more effective than progestin-only pills at preventing pregnancy, but it is more expensive.
Because ECPs are used for only a short time, most women—including some who have been told by a doctor that they shouldn’t take birth control pills—can safely take them. If you have a serious health problem that prevents you from taking regular birth control pills, consult a health-care provider. Certain medications may interfere with Ella, so discuss any other medications you’re taking with your provider.
If you could be pregnant already, it is a good idea to take a pregnancy test before using emergency contraception. ECPs should not be used by women who are already pregnant—not because the pills are thought to be harmful, but because they are ineffective at terminating established pregnancies. If after taking the pills you become pregnant anyway, there is no evidence of danger to the fetus.
How to Use
Some people call emergency contraceptive pills “morning-after pills.” But you do not have to wait until the morning after. You can start the pills right away or up to five days after you have had unprotected intercourse—that is, intercourse during which you did not use birth control or your birth control may have failed. The sooner progestin-only or progestin-plus-estrogen ECPs are started within the five-day (120-hour) window, the more effective they are. Ella, however, is equally effective on all five days after unprotected sex.
Plan B and Next Choice reduce the chance of pregnancy by 88 to 95 percent. If a hundred women have unprotected intercourse, about eight will become pregnant; if the one hundred women use Plan B, only one will become pregnant. Plan B is 89 percent effective for all women who take the pills within the first three days. Taking the pill within the first 24 hours may increase effectiveness to as much as 95 percent.
Combined estrogen and progestin pills are slightly less effective than progestin-only pills. They reduce the chance of pregnancy by 75 percent.
Ella reduces the risk of pregnancy by 98 percent. It is equally effective regardless of which day it is taken.
Progestin-only pills have few or no side effects. Nausea and vomiting are the most common negative effects of taking emergency contraception pills that contain both estrogen and progestin; about half the women who take them feel nauseated, and about 20 percent vomit. For this reason, some practitioners advise taking the pills with food or with an antinausea medication such as an over-the-counter remedy for motion sickness. Other negative effects include breast tenderness, dizziness, abdominal pain, and headaches. Using combination pills for emergency contraception may also change the timing of your next menstrual period: It may begin a few days earlier or a few days later than usual.
The most common side effects of Ella are abdominal pain, cramping, and irregular bleeding. Less common side effects include headache and nausea.