Emergency contraceptive pills (commonly known as “The Morning After Pill”) are used to prevent pregnancy for up to 72 hours after unprotected sex. Plan B, the most widely available emergency contraceptive, is cost efficient, available over-the-counter and has been approved for safe use in all women of child-bearing age (i.e. all women who have begun to menstruate).
Plan B’s mechanism of action is not entirely understood. One thing that is becoming clearer is that one statement on the packaging of these pills may be wrong: top medical scientists believe that emergency contraceptives do not block fertilized eggs from implanting on the uterus.
The official website for Plan B, the brand name form of levenorgestrel tablets, states that the medication works mainly by stopping ovulation (the release of an egg from the ovary). Essentially, the medication stalls the release of an egg until it is too late for the sperm to fertilize it. The website goes on to say that Plan B may also work by preventing the fertilization of an egg and preventing the attachment of an already-fertilized egg to the uterus. It’s this last statement with which many leading scientists take issue.
In 2012, The New York Times reported that the phrasing on Plan B labels and several respected medical websites is not congruent with what scientists know about how emergency contraceptives work. Scientists have found that these pills do delay ovulation, and that some varieties of the Morning After pill also thicken the cervical mucus, which reduces the chance of sperm reaching and fertilizing an egg. These scientists have found no evidence, however, that these pills prevent a fertilized egg from attaching to the uterus.
The original FDA description for Plan B is vague, and states that the drug “could theoretically prevent pregnancy by interfering with a number of physiological processes”, including implantation. Experts believe the reason implantation was originally included in this list is because Plan B contains levonorgestrel, an ingredient in many daily birth control pills, alters the lining of the uterus.
However, this alteration has not been proven to prevent implantation.
Regardless of Plan B’s mechanism of action, it is important to remember that this medication is more effective the sooner it is taken after unprotected sex, and it will not terminate a pregnancy once a fertilized egg has attached to the uterine wall. This medication also should not be used as a regular form of birth control, as it is not as effective as birth control medications that are prescribed for daily use.