Emergency contraception may be used to prevent pregnancy for a short period of time after unprotected sex.
Emergency contraception decreases the chance of pregnancy after one episode of unprotected intercourse, including when the act occurs near the time the egg is released (ovulation)—when conception is most likely. Overall, the chance of pregnancy is about 5% after one episode of unprotected sex, but closer to ovulation, it is about 20 to 30%. The sooner emergency contraception is used, the more likely it is to be effective.
Available options for emergency contraception include medications taken by mouth and a copper intrauterine device (IUD). These medications (the so-called morning-after pills) include levonorgestrel, ulipristal acetate, and combination oral contraceptions (estrogen plus levonorgestrel). They inhibit or delay ovulation. They are more commonly used as emergency contraception than are IUDs, even though a copper intrauterine device Intrauterine Devices (IUDs) Intrauterine devices (IUDs) are small, flexible, T-shaped plastic devices that are inserted into the uterus. In the United States, 12% of women who use contraception use IUDs. IUDs are popular... read more is the most effective form of emergency contraception. The copper IUD prevents the fertilized egg from implanting in the uterus.
Insertion of a copper IUD: To be effective, the IUD must be inserted within 5 days of unprotected sex or, if the time of ovulation can be estimated, within 5 days of ovulation (release of an egg from the ovary). The chance of pregnancy after insertion of the IUD is 0.1%—the same as it is when the IUD is used for regular birth control. Also, after its insertion, the IUD can be left in place to provide continued contraception for up to 10 years. The effectiveness of a copper IUD as emergency contraception is not affected by weight. Thus, in women who are obese who strongly desire to avoid pregnancy, the copper IUD is the preferred method for emergency contraception.
Insertion of a high-dose levonorgestrel-releasing IUD: To be effective, this IUD should be inserted within 5 days of unprotected sex or, if the time of ovulation can be estimated, within 5 days of ovulation. The chance for pregnancy after insertion of this IUD is 0.3%.
Ulipristal acetate: One dose of this medication is taken. It is more effective than levonorgestrel. It must be taken within 5 days (120 hours) after unprotected intercourse. The chance of pregnancy is about 1.5%. Ulipristal acetate is more effective than levonorgestrel for women who are obese, but having obesity decreases its effectiveness. A prescription is needed. After women take ulipristal acetate, they must wait 6 days before using a hormonal contraceptive that contains a progestin. They should use a backup method of contraception (such as a condom) for 7 days after starting to use the hormonal contraceptive.
Levonorgestrel taken by mouth: Levonorgestrel is most commonly used. It is a progestin often taken in lower doses for contraception. Women may take a dose, followed by another dose 12 hours later. Or they may take one higher dose. The chance of pregnancy is about 2 to 3%. However, levonorgestrel emergency contraception may be less effective in women who are obese. The dose is more effective the sooner it is taken. It must be taken within 5 days (120 hours) after unprotected intercourse (although it is less effective if taken after 3 days). In the United States, these pills are available over-the-counter without restriction for women of all ages who have had unprotected intercourse. A hormonal contraceptive may be started at the same time. A backup method (such as a condom) is recommended for 7 days after starting to use the hormonal contraceptive.
Yuzpe method: For this method, a combination oral contraceptive—ethinyl estradiol (a form of estrogen) plus levonorgestrel—is used, but it is slightly less effective than levonorgestrel or ulipristal acetate. Two combination pills are taken, followed by two more pills 12 hours later but taken within 72 hours of unprotected sex. A high dose of estrogen is used. The high dose often causes nausea and sometimes causes vomiting. Doctors may recommend medications that can help prevent nausea and vomiting. This method is less effective than other methods and is used only when women do not have access to other methods. A hormonal contraceptive may be started at the same time. A backup method (such as a condom) is recommended for 7 days after starting to use the hormonal contraceptive.
A pregnancy test is done 2 to 3 weeks after emergency contraception is used to make sure the woman is not pregnant. Resumption of menstrual periods and a negative pregnancy test result confirms that the woman is not pregnant.