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According to the definition given by the American College of Obstetricians and Gynecologists, pregnancy is the implantation of a preembryo in the uterine wall. Nonetheless, the question of when human life begins continues to be debated in very public-and very political-arenas. That debate has led to some misconceptions about what the drug actually does.


The hormonal emergency contraception available to women in the United States, often called "the morning-after pill," is a progestin-only drug made by Barr Manufacturing and marketed as Plan B. It reduces the risk of pregnancy up to 75% when the first of several doses is taken within 72 hours of unprotected intercourse. (It's most effective, however, when the first dose is taken within 24 hours.) Its exact action isn't known, although it's thought to block three crucial physiologic processes: ovulation, fertilization, and implantation of the preembryo in the uterine lining. The drug has no effect on an established pregnancy.

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Seven states-Alaska, California, Hawaii, Maine, New Hampshire, New Mexico, and Washington-allow pharmacists with special training to sell Plan B without a prescription. In late August, the U.S. Food and Drug Administration postponed making a decision on whether Plan B will be made available over the counter in U.S. pharmacies.


Some clinicians have worried that emergency contraception will result in a rise in its use as a primary method of birth control. But in the United Kingdom, where emergency contraception has been available over the counter since 2001, that does not seem to be the case. According to a study by Marston and colleagues published in the July 30 issue of the British Medical Journal: "Making emergency hormonal contraception available over the counter does not seem to have led to an increase in its use, to an increase in unprotected sex, or to a decrease in the use of more reliable methods of contraception."