Plan B: How Does the Morning After Pill Work?

Accidents happen: a condom breaks, or it can slip off. Maybe neglected to use one at all. Whatever the scenario, you've had unprotected sex and now may be facing an unwanted pregnancy. For these emergency situations, there is a way to prevent it—but you need to act fairly quickly. It's called the Plan B emergency contraceptive, and if you're over 18 years old, you can easily obtain it without a prescription.

"It's called the morning-after pill but it can be somewhat effective up to five days later," says Jennifer Wu, MD, of Lenox Hill Hospital in New York City. "I've had patients come back five days after a vacation and take it, and it works."

Plan B Basics

● Also called the morning-after pill, it contains 1.5 mg of progesterone, the female hormone that is also contained (in lower doses) in oral contraceptives.

● Plan B works by altering the lining of a woman's uterus and making the cervical mucus hostile to sperm, Wu explains. All told, it's about 98 percent effective, but its effectiveness depends somewhat upon when you take it. "For a woman at her most fertile, it will not work quite as well as at another time when she is not so fertile," Wu says.

● It's available over the counter, though women under 18 need a prescription. "So if you are under 18, you may want to ask your doctor for an undated prescription," Wu says.

● If a pregnancy has already implanted, Plan B has no effect on it. "It will not harm the developing baby," says Stephen Lindheim, MD, a reproductive endocrinologist at the University of Cincinnati in Cincinnati, Ohio.

● Last December, Plan B drew a lot of publicity when Secretary of the Health and Human Services Department Kathleen Sebelius overruled an Food and Drug Administration (FDA) ruling that Plan B was safe to sell over the counter. Until then, no health secretary had ever overruled the FDA. Sebelius contested that the manufacturer of Plan B had not adequately studied whether it was safe for girls as young as 11 to use.

● For every eight potential unwanted pregnancies, seven could be prevented with Plan B, says Lindheim. "It could be helpful in cases of rape or if a condom breaks," he says. "But it is not meant to be longterm birth control."

● If you have an ectopic pregnancy, Plan B will not be effective, Lindheim says.

● A side effect of the medication can be nausea.


"Kathleen Sebelius." Biography. 8 December 2011. Times Topics. The New York Times.

Plan B (Contraceptive). 9 December 2011. Times Topics. The New York Times.