image Unintended pregnancy is surprisingly common. At least half of all pregnancies in the United States each year are mistimed or unplanned, because birth control measures weren't used or those that were used did not work. Several years ago, the FDA approved a new type of contraceptive pill to provide women another option in preventing unintended pregnancy

It's considered one of the best-kept secrets of reproductive medicine, but emergency contraception is not new. Since 1974, the FDA has studied the use of oral contraceptives (birth control pills) for emergency use as so-called morning-after pills. Oral contraceptives have been used for years for that purpose and the FDA endorses the use of specific brands for emergency use, but in the past several years, products have been developed specifically for use only in an emergency.

The current first choice, known as Plan B, consists of two tablets of a progestogen hormone. A woman should take the first tablet as soon as possible (up to 72 hours) after unprotected sex. The second follows 12 hours later (many providers recommend taking both tablets at the same time). Plan B prevents pregnancy in a variety of ways. Depending on the time of the month in a woman's cycle, the drug may prevent ovulation (release of the egg from the ovary), interfere with fertilization, or prevent a fertilized egg from attaching in the uterus. Plan B will not induce an abortion if a woman is already pregnant, according to the definition of pregnancy used by the National Institutes of Health and the American Congress of Obstetricians and Gynecologists.

Pregnancy Prevention—Nearly 90%

Various sources put the rate of unintended pregnancy between 50%-60%, with 30%-50% of these ending in abortion.

If taken within 72 hours, Plan B reduces the chance of pregnancy by almost 90% after one act of unprotected sex. The sooner treatment begins, the more likely Plan B is to be effective. Nearly 95% of all pregnancies can be prevented if treatment begins within the first 24 hours after sex.

But some health experts have reservations about the use of emergency contraception. "I'm concerned that women will rely on this method and not take normal precautions," says Kathleen Winfield, a public health nurse in New Jersey who specializes in the prevention of infectious diseases. The convenience of swallowing two pills may indeed be attractive to those who might otherwise use a barrier method of contraception, like a condom, that helps prevent the spread of HIV and some other sexually transmitted diseases. However, studies done to evaluate this very issue have repeatedly shown that immediate access to emergency contraception does not alter a woman’s (or adolescent’s) sexual behavior nor contraception choices.

Two Pills, Less Nausea

Oral contraceptives fall into two categories: 1) pills containing a mix of progestin and estrogen (combination pills); 2) or those with progestin only. Both types of pills effectively block conception when used for regular birth control. For emergency measures, a woman takes two pills in 24 hours to flood the system with excess hormones. Progestin-only tablets have the benefit of minimizing the stomach upset that combination pills can cause when used in emergencies. But until Plan B was approved, women wishing to avoid estrogen and its unpleasant side effects had to take 40 progestin-only pills for emergency use. Plan B contains more progestin than traditional contraception pills, which is why only two pills do the job that previously required 40.

Approximately 33%-50% of women who take estrogen-progestin pills for emergency use experience nausea, whereas only 23% of women taking Plan B reported nausea. Vomiting is also a less common side effect with Plan B (6% versus 20% in those taking combination pills).

After taking Plan B, most women will have a normal period at the expected time, give or take seven days. Heavier than usual bleeding occurs in roughly 12% of users, while around the same percentage of women experience a lighter flow. A few women notice spotting a few days after use. If a period doesn't start when expected, a pregnancy test should be performed.

Other Emergency Contraceptives

The Yuzpe regimen, named after its creator, is a longstanding standard emergency contraception protocol used with ordinary contraceptive estrogen-progestin pills. This regimen allows doctors to prescribe taking multiple pills of almost any birth control pill, with the exact number depending on the brand of pill. The treatment schedule is usually one dose within 72 hours after unprotected intercourse and another dose 12 hours later.

Where to Get Emergency Contraception

Since 2006, adult women can obtain Plan B at any pharmacy, without a prescription. Women 17 and under must have a prescription. You can obtain a prescription through Planned Parenthood and most healthcare providers. To identify a clinic or pharmacy that carries emergency contraception, call your physician or the Emergency Contraception Hotline at 1-888-NOT-2-LATE.