Here's what happens in your body when you take emergency contraception and why it's totally different than abortion

The Supreme Court is poised this week to hear oral arguments in another major challenge to the contraception mandate in the Affordable Care Act. This means, inevitably, that there will be an uptick in the amount of false or otherwise misleading information about birth control making the rounds as the case gets covered.

Like this news release, from Priests for Life, one of the plaintiffs in Zubik v. Burwell:

Priests for Life objects to the contraceptive and abortion-causing drugs and devices covered by the HHS mandate because they are counter to Catholic teaching. But we also oppose being ordered to provide our employees with substances that are so clearly harmful to women.

But before we get into the science of birth control, let’s start with the basics about the case: the Affordable Care Act requires all insurance companies to cover contraception without a copay, which is good news for the millions of women in the United States who use birth control because birth control can be pretty expensive. (Getting an IUD inserted can cost up to $1,000, which is almost an entire month’s pay if you’re earning the minimum wage.)

The law also contains an accommodation for religiously-affiliated employers that say they object to covering birth control through their own plans. That provision allows these organizations to opt out of directly providing the coverage so that the Department of Health and Human Services can arrange it instead. It was designed as a workaround so that organizations like Priests for Life could opt out of covering birth control while employees of Priests for Life who may want to use birth control could still get it without a copay.

But the groups challenging the law claim that this accommodation—essentially notifying the government that you don’t want to cover birth control under your insurance—is still a violation of their core religious beliefs because, at the end of the day, employees can still access birth control.

And while Priests for Life objects to all forms of birth control, they also claim that emergency contraception is the same thing as medication that causes abortion.

It’s not.

In order to get the science down, I reached out to Dr. Tracey Wilkinson, a pediatrician and reproductive health researcher in Indianapolis, Ind., to walk through the medical facts about contraception, abortion, and pregnancy.

So here are the basics about what happens in your body when you take emergency contraception and during a medication abortion, and why the two are totally different no matter what you might read or hear in the coming days and weeks.

What is emergency contraception?

It’s birth control. Or more specifically, emergency contraception is a big category of different kinds of birth control that you can take if your primary birth control method fails—broken condoms, forgotten pills—or if you just didn’t use any to begin with. The most common form in the United States is Plan B One-Step (some people call it the morning after pill), and you can buy it over-the-counter.

But there are other kinds of emergency contraception. A copper IUD, when inserted within five days of unprotected sex, can work as a method of emergency contraception (as well as long-acting contraception after the fact). There is also something on the market called ella (yes, the lowercase “e” is part of the marketing), which is still prescription-only.

But the biggest thing to remember about over-the-counter emergency contraception pills, according to Wilkinson, is that it’s preventative. Adding the word “emergency” tends to throw some people off, but it’s still just birth control.

“There is nothing about emergency contraceptive pills that end a pregnancy,” she told me. “There has been a lot of research done on the mechanisms behind emergency contraception, and all of it shows that it does not affect an existing pregnancy.”

OK, how does Plan B actually work?

When you take Plan B or a generic progestin-only pill, you are actually taking a high dose of progesterone, which is the same stuff that is in the kind of birth control pills that some people take every day. The high dose of progesterone can thicken the cervical mucus, which makes it harder for the sperm to get to the egg. And if you haven’t ovulated—ovulation is when the ovary releases an egg—it can delay the process, which is another way to keep sperm from reaching the egg.

Preventing or delaying ovulation is the primary mechanism by which Plan B prevents pregnancy. Without ovulation, there can be no fertilization. Without fertilization, there can’t be implantation in the uterus, which is the thing that triggers the hormones that let your body know you are pregnant.

So what happens if you take over-the-counter emergency contraception pills after you’re already pregnant?

Nothing. Nothing happens.

So what’s the deal with ella? Is that different than Plan B?

Ella contains the hormone ulipristal acetate and is only available with a prescription. The good thing about ella, Wilkinson says, is that it works just as well on day one or day five after unprotected sex.

While Plan B works by tricking your body into thinking it’s already pregnant, allowing for its pregnancy prevention reactions to kick in; ella suppresses progesterone, which delays ovulation. That buys your body extra time to allow the sperm to die—sperm can survive for several days inside a woman’s reproductive tract—before it has a chance to meet with an egg.

And what’s the deal with the copper IUD?

There are two types of Intra-Uterine-Devices (or IUDs) out there: hormonal IUDs that have a low dose of hormone, or the copper IUD. “As the name suggests,” Wilkinson says, “there’s copper in it.” It is the most effective form of emergency contraception on the market.

When used as long-acting birth control, the copper IUD, a small device implanted in the uterus, acts as a kind of ultimate sperm destroyer. The copper ions kill the sperm before it has a chance to reach an egg, which is conceptually pretty cool if you think about it.

If it’s long-acting birth control, why would anyone use it as emergency contraception?

For one thing, it can be hard to coordinate, which is why Wilkinson says it’s rare for people to use copper IUDs as emergency contraception. But it’s possible.

The copper IUD requires some advanced planning—and a doctor’s visit—to have implanted. If someone’s primary method of birth control fails, they may not be able to get an appointment to get an IUD placed within the five-day window they have to avoid pregnancy.

But they’re really effective. So if the stars line up and you happen to have an appointment already or can make an appointment in time, they’re an excellent option, Wilkinson says.

“The main way a copper IUD works as emergency contraception is to make it harder for sperm to survive. It also causes irritation to the uterine lining that makes implantation difficult,” Wilkinson explains. “So there is a chance that if you have a fertilized egg coming down the fallopian tube that, if you insert a copper IUD, it would make it harder for that egg to implant.”

Medical consensus holds that The copper IUD, when used as emergency contraception, is the only method of emergency contraception that may impact implantation. The Association of Reproductive Health Professionals has a useful chart on how all of this works (“ECPs” means “emergency contraception pills”):

Now what about the abortion pill?

Like we talked about before, none of these methods of emergency contraception will work after you’re already pregnant. If you’re already pregnant and don’t want to be, one of the ways you can end the pregnancy is through a medication abortion, which is sometimes called the abortion pill.

So it’s just one pill?

In the United States, it’s actually two pills. First, you take mifepristone, which is the generic name of the medication that actually terminates the pregnancy.

Wilkinson calls progesterone the “pro-pregnancy hormone.” Whereas Plan B mimics the effects of progesterone in the body, mifepristone blocks progesterone from working. “So if your body needs progesterone to maintain a pregnancy and you take a medicine that blocks it, that’s why it causes the pregnancy to end,” Wilkinson said.

The second medicine you’ll take is called misoprostol, which causes cervical dilation and contractions to expel that pregnancy. “It’s a two-step process,” Wilkinson explained. “So you’ll usually take misoprostol, the medication that expels the pregnancy, 24 to 48 hours after you take the first medicine, mifepristone, the medication that blocks progesterone and causes the pregnancy to end.” You can take it up to nine weeks into a pregnancy, and you can take the medicines at home.

So medication abortion is not the same thing as emergency contraception.

Right. The mechanisms are just totally different.

Remember: Plan B is a high dose of the hormone, progesterone, that your body needs to maintain a pregnancy. (That’s why it’s OK to take it if you’re already pregnant: it’s just a high dose of the hormone your body is already producing.)

Medication abortion is mifepristone, which blocks progesterone from working. That’s what causes an existing pregnancy to fail.

So when someone claims that emergency contraception is an abortion-inducing drug…