The Science of Contraception
Plan B has made front-page news recently, with reports that some pro-life pharmacists are refusing to fill prescriptions for emergency contraception because they believe the drugs cause abortion. Fourteen states have drafted legislation that would allow pharmacists to decline to dispense emergency contraception; one bill passed in Arizona but was vetoed by the governor.
Several articles published in the scientific journals Contraception and Human Reproduction have found in rats, monkeys and humans that Plan B, or levonogestrel (the active ingredient in levonogestrel is progestin), prevents ovulation without interfering with fertilized eggs.
In contrast, mifepristone, known as Mifeprex or RU-486, is a drug that will induce abortion in the first 49 days of gestation. FDA regulations require that women take the drug only under a doctor's supervision. Another drug, methotrexate, was originally developed to treat cancer and is also sometimes used to induce abortion.
The studies cited by The Population Council this week looked specifically at the effects of levonogestrel.
Women can get pregnant if they have unprotected sex before ovulation, since sperm can live for up to five days. But an egg is usually viable for only six to 12 hours after it is released from the ovary. Plan B works by suppressing the hormonal surge that causes an ovary to release an egg. It must be taken within 72 hours after intercourse, followed by another tablet 12 hours later. If a woman takes the drug after the egg has already been released, it won't stave off fertilization or end a pregnancy, according to the studies and the manufacturer, Barr Pharmaceuticals.
Yet news reports as well as Pharmacists for Life say the drug can cause abortion by preventing a fertilized egg from implanting in the uterus. Members of Pharmacists for Life did not respond to phone calls and e-mails, but the group's website calls Plan B "a progestin-only abortifacient which prevents implantation as a major mechanism of action."
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