You’ve heard them mistaken for each other before. On the news, in social circles, and even in some medical arenas, emergency contraception is stigmatized, mislabeled, and misconstrued as an entirely different drug--"the abortion pill.” While they’re both used by women not wishing to be pregnant, the reality is that these are very different drugs, without much else in common. One acts to stop an already growing pregnancy (the abortion pill, RU-486, or mifepristone) and the other prevents pregnancy from ever occurring (emergency contraception). The confusion however, is not entirely the fault of anti-choice zealots, but instead, the result of a baseline lack of public awareness of birth control options in general.
Last week, when the United States Food and Drug Administration announced its approval of the new 5-day emergency contraception pill, Ella, scheduled for release in the U.S. late in the fall of 2010, it wasn’t long before anti-choice groups began condoning its use, and an under-informed audience began listening to these faulty words of caution.
The key to preventing this misunderstanding, is to remember that fertilization is not a one-step process. Sperm take hours, even days, to encounter an awaiting egg, and any disturbance along the way--impaired sperm motility, harsh intrauterine environments, blocked or congested fallopian tubes, or impenetrable eggs--can make the fertilization process increasingly difficult, even impossible. Despite stories about young girls getting pregnant after only their first sexual encounter, fertilization is truly a finicky process, where timing is everything and a multitude of conditions need to be right.
This is where the differences between the abortion pill and emergency contraception become unmistakably clear. Mifepristone works by stopping something that has already occurred. It’s an anti-progesterone, which means that it antagonizes progesterone’s stabilizing effect on the implanting embryo in the uterine wall. If the embryo’s surrounding sac can’t effectively attach to the inside of the uterus, then the embryo cannot continue to receive blood supply and grow. Used at around nine weeks or less in the U.S. for first trimester abortions only, mifepristone essentially clears the uterus of the developing pregnancy tissues. It also helps open the cervix and release factors that help the uterus contract.
Emergency contraceptive pills act before implantation and before the sperm and egg even join. The most widely popular pill in the U.S., Plan B, is a progesterone only pill (levonorgestrel) that works by inhibiting ovulation from occurring. If the egg is never released, you can’t get pregnant. There were studies in the 1970s and 80s looking at possible implantation inhibition as well (stopping an already formed zygote from getting to its nesting place in the uterus), but later research found these trials less plausible, suggesting that the more likely mechanism is interference with ovulation and fertilization. Emergency contraception pills are hormones--estrogen and progesterone or progesterone alone--while mifepristone/”the abortion pill” is an anti-hormone. The “morning after pill” is therefore medically and legally an entirely different class of medication--a contraceptive.
To find out more about these differences and about the new 5-day emergency contraceptive, Ella, please see the links below.
1. Mifepristone, aka RU-486, aka "The abortion pill"
2. Plan B or levonorgestrel, aka emergency contraception, aka "The morning after pill"