How Plan B works and why it’s not abortion

Since the U.S. Supreme Court’s overthrow of Roe v. Wade, who ended nearly five decades of a precedent that protected the constitutional right to an abortion, there has been much public debate and confusion about what constitutes an abortion and what is considered legal.

Emergency contraceptives such as Plan B, also known as the morning-after pill, which is taken to prevent pregnancy after unprotected intercourse, have also been falsely interpreted by some as a form of abortion.

With no exact consensus, some states have defined “life” as beginning at conception or fertilization – the moment that egg meets sperm. Meanwhile, the American College of Obstetricians and Gynecologists (ACOG) – the country’s leading medical group for OB-GYNs – says complex medical concepts are being “abused” by state lawmakers.

PHOTO: A package of Plan B contraceptives will be displayed on April 5, 2013 at a pharmacy in San Anselmo, California.

A package of Plan B contraceptives will be on display on April 5, 2013 at a pharmacy in San Anselmo, California.

Justin Sullivan / Getty Images, File

“Fertilization and pregnancy are not the same thing,” said Dr. Elizabeth Schmidt, assistant professor of obstetrics and gynecology and director of family planning at North Shore University Hospital in New York, said. “Fertilization is not a medically recognized term.”

But doctors say the debate over when to start life should not have any bearing on Plan B, which works to stop pregnancy even earlier in the process – before conception, or conception.

What is Plan B?

Plan B is a progesterone hormone, which prevents ovulation or the release of an egg when taken at the right time. It effectively prevents fertilization or the encounter of the sperm and egg for pregnancy. If taken after ovulation has already taken place, Plan B has no effect and there is no evidence that it harms an already established pregnancy, according to ACOG.

“Pregnant people make progesterone, and Plan B is a type of progesterone, so it makes sense that it would have no effect on a developing embryo,” Schmidt told ABC News.

Why is it confused with abortion?

Some of the confusion may stem from the Food and Drug Administration’s own website, which explains that Plan B “can prevent a fertilized egg from attaching to the uterus (implantation).” The problem, experts say, is that this description is inaccurate.

When the FDA first approved emergency contraception in the late 1990s, it was not entirely clear how the pills prevented pregnancy, says Susan F. Wood, Ph.D., George Washington University professor and former director of the FDA’s Office for Women’s Health.

Now, she said, “new evidence [that has] which has been around for about 10 years now, has shown that Plan B actually works, probably essentially just through that first mechanism – which blocks ovulation. “

Yet the FDA’s statement was interpreted by some to imply abortion, which led to objections to Plan B.

How does Plan B work?

“When used as an emergency contraception, Plan B only affects ovulation,” Schmidt said. “Studies have failed to show any effect of levonorgestrel on uterine lining when used as a single dose in emergency contraception.”

In a 2001 study published in Contraception, scientists looked at 45 women treated with short-term levonorgestrel administration – the same hormone found in Plan B – and no attenuation in the uterus was observed or levonorgestrel administered to or thereafter ovulation. Previous studies in monkeys and rats have also failed to show a significant effect of the levonorgestrel hormone on uterine lining to prevent the implantation of a fertilized egg.

Taken together, this evidence suggests that Plan B works primarily on the first step in the process – to prevent the body from releasing or ovulating an egg in the first place.

If the body has already released an egg before taking Plan B, the drug does not stop an egg from meeting sperm, and it does nothing to prevent a fertilized egg from implanting in the uterus.

Wood said given the current legal environment, the FDA should consider updating the language on its website “to pull Plan B out of the firing line” of anti-abortion groups.

When ABC News reached out for comment, an FDA spokesman did not comment directly on the language on its website, but stressed that “emergency contraception is used to reduce the chance of pregnancy after unprotected sex.”

“Plan B is an extremely safe medication and there are no medical contraindications to its use. It is safer than Tylenol – which is sold over the counter without restriction,” Schmidt said.

Although contraception is currently legal throughout the US, the growing abortion restrictions in the country now address some forms of contraception.

In his corresponding opinion on the overthrow of Roe v. Wade, Supreme Court Justice Clarence Thomas wrote that the court should reconsider other “demonstrably erroneous” precedents in the future, including the 1965 judgment in Griswold v. Connecticut, which recognizes the right of married couples to purchase and use contraceptives without government restriction.

“Restricting access to any medical care can have disastrous effects on communities,” Schmidt said. “It has been shown that states with limited access to abortion also have higher rates of maternal and infant mortality. The situation will be exacerbated by banning access to emergency contraception and abortion, which will excessively hurt the most vulnerable and disadvantaged.”

Dr. Esra Demirel is a Fellow in Minimally Invasive Gynecological Surgery at NYU Langone Health and is a contributor to the ABC News Medical Unit.

ABC News’ Anne Flaherty contributed to this report.

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