Labels inside every box of morning-after pills -- drugs widely used to prevent pregnancy after sex -- say they may work by blocking fertilized eggs from implanting in a woman's uterus. Respected medical authorities, including the National Institutes of Health and the Mayo Clinic, have said the same thing.
Such descriptions are kindling in the abortion debate.
Based on the belief that a fertilized egg is a person, some religious groups and conservative politicians say disrupting a fertilized egg's ability to attach to the uterus is abortion, "the moral equivalent of homicide," said Dr. Donna Harrison, who directs research for the American Association of Pro-life Obstetricians and Gynecologists.
But an examination by the New York Times has found that the federally approved labels and medical websites don't reflect what the science shows. Studies have not established that emergency contraceptive pills prevent fertilized eggs from implanting in the womb, leading scientists say. Rather, the pills delay ovulation, the release of eggs from ovaries that occurs before eggs are fertilized.
It turns out that the politically charged debate over morning-after pills and abortion is probably rooted in outdated or incorrect scientific guesses about how the pills work. Because they block creation of fertilized eggs, they would not meet abortion opponents' definition of abortion-inducing drugs. In contrast, RU-486 is an abortion pill because it destroys implanted embryos.
The implantation idea stems from the Food and Drug Administration's decision during the drug-approval process to mention that possibility on the label -- despite lack of scientific proof and objections by the manufacturer of Plan B, the pill on the market the longest. Leading scientists say studies since then provide strong evidence that Plan B does not prevent implantation and no proof that a newer type of pill, Ella, does.
After the Times asked, ADAM, the firm that writes entries for the NIH website, deleted passages suggesting emergency contraceptives could disrupt implantation. The Times, which uses ADAM's content on its health webpage, updated its site. The medical editor-in-chief of Mayo's website, Dr. Roger Harms, said "we are champing at the bit" to revise the entry if the FDA changes labels or other agencies make official pronouncements.
"These medications are there to prevent or delay ovulation," said Dr. Petra Casey, an obstetrician-gynecologist at Mayo. "They don't act after fertilization."