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Emergency hormonal contraception (the "morning after pill")

Emergency hormonal contraception is sometimes called "the morning after pill." It is actually a short course of the hormones found in oral contraceptives taken at a high dose. The exact regimen (the number of pills and the number of days) depends on the type of oral contraceptive used.

Depending upon the time during the menstrual cycle that the emergency contraceptives are taken, these may prevent pregnancy by blocking the implantation of the fertilized egg in the uterus, by inhibiting ovulation, or by interfering with fertilization of the egg. To be considered a possible candidate for emergency contraceptive pills a woman should receive medical attention within 72 hours of unprotected intercourse. The pills are most effective when taken as soon as possible after unprotected intercourse. (In contrast, emergency contraception with an IUD may be possible 5 days after intercourse, see below.) The only known contraindication to emergency contraception is pregnancy. So a woman must not be pregnant when these methods are used. Emergency hormonal contraception may be taken on any day of the menstrual cycle. Emergency hormonal contraception is available in the US for people aged 17 or older (proof of ID is required for purchase). It is also available for younger teens with parental permission.

Neither a physical examination, nor any laboratory tests are required prior to use of the emergency hormonal contraception. It can be taken at any time during the menstrual cycle, and the next menstrual period typically occurs within one week of the expected time. The timing of the subsequent menses is to some extent dependant upon the time in the cycle at which the emergency contraceptive was taken.

There are no serious side effects, but the pills may cause nausea in 30% to 50% and vomiting in 15% to 20% of women. These side effects may be controlled by taking an anti-nausea drug such as dimenhydrinate (Dramamine). Frequently a doctor will give a prescription nausea medication, such as prochlorperazine(Compazine), at the same time as the emergency contraceptive pill. A woman may also experience breast tenderness and a temporary disruption of her menstrual cycle.

The most common type of emergency hormonal contraception involves the administration of the progesterone hormone levonorgestrel in two doses (marketed as Plan B in the U.S.). Another formulation for emergency hormonal contraception uses estrogen along with levonorgestrel, but levonorgestrel-only medication may be more effective and causes less nausea compared to estrogen-containing products.

Clinical trials using low doses of mifepristone (known earlier as RU-486, sometimes called "the abortion pill") have shown that this agent is extremely effective as an emergency contraceptive when taken prior to ovulation, but it has not been approved for this use. Mifepristone (Mifeprex) has been approved, in much higher doses, for terminating a pregnancy of less than 49 days' duration and must be taken under a physician's supervision.

Another type of anti-progestin medication that is similar to mifepristone in its structure and actions is known as ulipristal acetate. Ulipristal acetate (Ella) is marketed for emergency contraception in Europe and was approved by the US FDA in August 2010 for use in the US for emergency contraception up to 120 hours after intercourse.

Although effectiveness of the oral contraceptives are dependent to some extent upon how soon after unprotected intercourse they are taken, efficacy studies have generally reported pregnancy rates of 0.2% to 3% with use of oral emergency contraception.

Emergency contraceptive pills do not protect women from sexually transmitted infections (STDs).

This strategy is not meant to be a primary birth control method. Once the emergency is over, a woman should receive proper counseling so that she can select an effective and appropriate contraceptive method to use on a regular basis if she continues to be sexually active.