It turns out that the politically charged debate over morning-after pills and abortion, a divisive issue in this election year, is probably rooted in outdated or incorrect scientific guesses about how the pills work.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 opponentsÂ’ definition of abortion-inducing drugs. In contrast, RU-486, a medication prescribed for terminating pregnancies, destroys implanted embryos.
The notion that morning-after pills prevent eggs from implanting 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, scientists say, 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. Some abortion opponents said they remain unconvinced.
After The Times asked about this issue, A.D.A.M., the firm that writes medical entries for the National Institutes of Health Web site, deleted passages suggesting emergency contraceptives could disrupt implantation. The Times, which uses A.D.A.M.’s content on its health Web page, updated its site. The medical editor in chief of the Web site for the Mayo Clinic, Dr. Roger W. Harms, said “we are champing at the bit” to revise the entry if the Food and Drug Administration changes labels or other agencies make official pronouncements.
“These medications are there to prevent or delay ovulation,” said Dr. Petra M. Casey, an obstetrician-gynecologist at Mayo. “They don’t act after fertilization.”
The F.D.A. declined to discuss decisions about the effect on implantation or to say whether it would consider revising labels. But Erica Jefferson, an F.D.A. spokeswoman, acknowledged: “The emerging data on Plan B suggest that it does not inhibit implantation. Less is known about Ella. However, some data suggest it also does not inhibit implantation.”
Scientists say the pills work up to five days after sex, primarily stalling an eggÂ’s release until sperm can no longer fertilize it. Although many people think sperm and egg unite immediately after sex, sperm need time to position themselves.