Emergency contraception is used after an act of unprotected sexual intercourse or after an occasion when a contraceptive method fails (for example, when a condom breaks).
Emergency contraception decreases the chance of pregnancy after one act 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 act 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 drugs taken by mouth and a copper intrauterine device (IUD). These drugs (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 (IUD) 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 within 7 days of release of an egg (ovulation). 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 obese women who strongly desire to avoid pregnancy, the copper IUD is the preferred method for emergency contraception.
Ulipristal acetate: One dose of this drug 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 obese women, but being obese decreases its effectiveness. A prescription is needed.
Levonorgestrel: Levonorgestrel is most commonly used. It is a progestin often taken in lower doses for contraception. Levonorgestrel is taken by mouth. 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). These tablets are available over-the-counter without restriction for women of all ages who have had unprotected intercourse.
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 tablets are taken, followed by two more tablets 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 drugs 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.