Plan B may be the best-named drug in the pharmacy. That's because the so-called "morning-after" pill isn't anybody's plan A.

But the story now is what the FDA plans to decide about the drug by the end of the month. Will the agency allow the drug to be sold over the counter?

Plan A is the plan in family planning — the plan for when or whether a couple wants to have a baby. When plan A fails — that is, when a condom breaks or when a couple has sex without using birth control — there's plan B.

Plan B is emergency contraception, commonly known as the morning-after pill. There are two FDA-approved emergency contraceptive products. One is Preven from Gynetics Inc. The other is Plan B from Barr Laboratories.

Get the Facts About Emergency Contraception

Politics vs. Science

In December 2003, a meeting of two FDA advisory panels voted 23-4 in favor of letting drugstores sell Plan B without a prescription. But in May 2004, the FDA did something rare. Against the advice of nearly all of its outside experts, it said Plan B must remain a prescription drug.

The FDA cited concerns that Plan B had not been tested in enough women under the age of 16. So in July 2004, Barr went back to the FDA, asking the federal agency to approve over-the-counter sales of Plan B for women 16 and older.

A decision on this application was expected last May. It didn't come. The American College of Obstetricians and Gynecologists accused the FDA of playing politics with a scientific decision.

Last month, Health and Human Services Secretary Michael O. Leavitt said the FDA would announce a decision by Sept. 1. Politics had a lot to do with that. Sen. Hillary Clinton, D-N.Y., and Sen. Patty Murray, D-Wash., placed a hold on the Bush administration's nominee for FDA chief. They said they'd release the hold when the FDA acted on Plan B, which they did when Leavitt declared the Sept. 1 target date.

Plan B, like any drug, has risks and benefits. What are they?

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How Plan B Works

Women who do not want to get pregnant should use plan A first. The most effective way to avoid pregnancy is not to have sex. The next most effective way, other than permanent sterilization, is contraception. This means using barrier contraceptives such as diaphragms or condoms, IUDs, or various forms of hormonal contraception.

All these forms of contraception prevent a man's sperm from fertilizing a woman's egg. Depending on where a woman is in her menstrual cycle, emergency contraception may work the same way. But it is more likely to work after sperm fertilizes the egg.

Just as a seed isn't considered planted until it's put in fertile ground, the vast majority of doctors say a baby isn't conceived until a fertile human egg is implanted in a woman's womb. That happens about seven days after sperm and egg come together and the resulting pre-embryo travels down the fallopian tubes to the womb. Plan B keeps the fertile egg from getting planted in the womb.

If Plan B does not work — if the egg does get planted in the womb — the pregnancy will proceed normally, says David M. Plourd, MD, assistant professor of obstetrics and gynecology at Naval Medical Center, San Diego.

"It is an all-or-none phenomenon: With Plan B, you either don't get pregnant or you do," Plourd says. "There is no in-between. Ether it works or it doesn't. If it doesn't work, there are no effects on the pregnancy; no miscarriage and no birth defects."

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How Well Does Plan B Work?

To prevent pregnancy, Plan B should be used as soon as possible after sex. That's why family planners encourage sexually active women who do not want to become pregnant to keep an emergency contraceptive in their medicine chest.

Theoretically, Plan B should work until the fertilized egg is implanted in the womb. It's been tested for up to five days, Plourd says — but it's strongly recommended that women use it within 72 hours of sex.

If 100 women have sex one time during a single menstrual cycle — without using any form of contraceptive — eight of them will get pregnant.

If those same 100 women take Plan B within 72 hours of sex, two of them will become pregnant. That, Plourd says, means it's 75 percent effective.

"Preventing pregnancy 75 percent of the time is less than almost every other form of contraception," Plourd says. "That is why it is plan B, not plan A."

Your Complete Guide to Birth Control

How Safe Is Plan B?

Julie A. Johnson, PharmD, chairwoman of the University of Florida department of pharmacy practice, was a member of the 2003 FDA advisory panel that voted to approve Plan B for over-the-counter sale.

"I've been on this committee, the Nonprescription Drug Advisory Committee, for almost four years, and I would take this to be the safest product that we have seen brought before us," Johnson said in a transcript of the panel meetings. Johnson voted with the majority for nonprescription approval.

Few argue that Plan B is unsafe for adult women. But some of the panelists expressed concern that the drug had not been tested in enough teenage girls. And panel chairman Louis R. Cantilena Jr., MD, PhD, worried that tests of Plan B — designed to mimic actual use of the drug — did not reflect the way the drug would be used in real-life nonprescription situations.

"My concern [with the Plan B actual-use safety study] is that it doesn't accurately reflect what will likely be the most common setting for this product based on what we've heard," Cantilena said in the transcript. "So the actual use [study] was not as close to possible to what we think will actually happen with the drug." Cantilena voted with the minority to disallow nonprescription sales of Plan B.

Panel member Susan A. Crockett, MD, a San Antonio ob-gyn, said in the transcript that she believed Plan B would decrease the number of planned abortions and that Plan B "is a health care advancement for women who have access to it." But she worried that over-the-counter sales would discourage women, especially young women, from seeing their doctors for birth control counseling.

"I'm going to go down kicking and screaming before I allow somebody to break that relationship between myself and my patients because I value the education component so much in that relationship I have with my patients," Crockett said. She voted against nonprescription sale of Plan B.

Plourd disagrees. "It is important for doctors to talk to patients," he says. "But it is patriarchal and cruel to women to withhold these pills until they come in to see me. Their primary need is to prevent that pregnancy. It is almost like coercion to say I won't prevent your pregnancy until you come in to my office."

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By Daniel J. DeNoon, Reviewed by Michael W. Smith, MD

SOURCES: American College of Obstetricians and Gynecologists. FDA. Planned Parenthood. Barr Laboratories. Transcript: U.S. FDA CDER Nonprescription Drugs Advisory Committee in Joint Session with the Advisory Committee for Reproductive Health Drugs, Dec. 16, 2003. David M. Plourd, MD, assistant professor of obstetrics & gynecology, Naval Medical Center; clinical instructor, University of California, San Diego.