What Happens When You Take Emergency Contraception

Last year, I was driving to my parents house the night before Thanksgiving when I suddenly realized that I'd forgotten to take two birth control pills in a row — and since that was the only form of contraception my (now ex) boyfriend and I were using at the time, I immediately panicked. The relationship hadn't been working for a while, and the last thing I needed or wanted was an unplanned pregnancy; so I took emergency contraception, and I'm really glad I did. However, though I knew at the time that it was effective, I wasn't actually aware of how emergency contraception works.

Most women who have heterosexual sex have endured a pregnancy scare or two in their lives. Sometimes these scares arise out of nothing more than post-sex paranoia; but in other cases (like mine), we just drop the ball where our own sexual health is concerned. Even if we always remember to use a condom or take our pill at the exact same time every day, we're usually not free from fear — because even condoms and birth control pills aren't 100 percent effective when they're used correctly. Fortunately, that's where emergency contraception (also called EC) comes in.

Of course, you definitely shouldn't be using emergency contraception as your regular form of birth control, no matter what — it's simply not as effective as the pill, condoms, IUDs, and other reliable birth control methods. But if you do need to take emergency contraception, you should know that it works well — it's 95 percent effective at preventing pregnancy when taken within 24 hours of unprotected sex, and 61 percent effective when taken within 48-72 hours of unprotected sex.

But you may have questions about emergency contraception beyond just how effective it is at preventing pregnancy — like, how does it prevent pregnancy? And how does it effect your body? Find answers to your burning questions below, as we examine five facts about how emergency contraception works to prevent pregnancy.

1. EC Can Prevent Pregnancy By Stopping The Ovary From Releasing An Egg

Contrary to what you may have heard, emergency contraception is not an abortion pill, and will not harm an existing pregnancy. Emergency contraception only works to prevent a pregnancy from happening in the first place. The main way it does this is by preventing the ovary from releasing an egg.

The primary ingredient in most emergency contraception pills is levonorgestrel, which is a synthetic version of the hormone progestin. (Levonorgestrel has been the main ingredient in most birth control pills for about 35 years, so you can rest assured that it's been tested quite a bit.) So it's basically just a super high dose birth control pill — and like regular birth control pills, an emergency contraception pill's primary action is to prevent your ovaries from releasing an egg. If no egg is released, no egg is fertilized, and thus no pregnancy occurs.

2. EC May Keep A Released Egg From Being Fertilized

However, if an egg has already been released from your ovary, emergency contraception can still take action to prevent pregnancy — it will work to prevent any sperm from fertilizing that egg. The dosage of levonorgestrel in the pill literally slows down both the egg and the sperm that's inside of you, making it far less likely that they'll meet up. Naturally, if your egg doesn't meet the sperm, it won't be fertilized, allowing you to successfully prevent pregnancy.

3. Some Believe That EC May Stop A Fertilized Egg From Attaching To Your Uterus — But There Is Scientific Disagreement About The Issue

According to most studies, emergency contraception is able to prevent pregnancy by preventing your ovaries from releasing an egg, or then keeping that egg from becoming fertilized. The National Institute of Health's U.S. National Library of Medicine page on emergency contraception states that EC works by "preventing or delaying the release of an egg from a woman's ovaries [or] [b]y preventing the sperm from fertilizing the egg."

The question of whether or not emergency contraception ever works by preventing a fertilized egg from implanting, however, is the source of much of the public controversy over the pill, much of it stemming from language on the pill's packaging and on the websites of various forms of emergency contraception. For example, the emergency contraception pill ella's website notes that "It’s also possible that ella works by preventing attachment to the wall inside the uterus." But many scientists now believe that this statement may not be accurate.

According to a website maintained by the Office of Population Research at Princeton University and the Association of Reproductive Health Professionals, "There is no evidence to suggest that either of the FDA-approved emergency contraceptive options, levonorgestrel (LNG, such as Plan B One-Step, Take Action, Next Choice One Dose or My Way ) or ulipristal acetate (UPA, such as ella) works after an egg is fertilized." The site then goes on, however, to note one study that "found that at certain doses, [certain brands of emergency contraception] can decrease the thickness of the endometrium (by 0.6 to 2.2 mm), but it is not clear that this would in fact prevent the implantation of a fertilized egg."

The New York Times reported in 2012 that "the [emergency contraception] pills delay ovulation, the release of eggs from ovaries that occurs before eggs are fertilized, and some pills also thicken cervical mucus so sperm have trouble swimming." The Times went on to note that

The notion that morning-after pills prevent eggs from implanting stems from the Food and Drug Administration’s decision during the drug-approval process to mention that possibility on the label — despite lack of scientific proof, scientists say...

All of this is to say that, while EC does prevent an egg from being fertilized, it's not totally clear whether or not it's actually capable of preventing the implantation of a fertilized egg.

4. EC Is Different From "The Abortion Pill"

There is a lot of confusion between emergency contraception and "the abortion pill." But taking emergency contraception is not the same thing as terminating a pregnancy — and if you need to terminate a pregnancy, don't make the mistake of thinking that emergency contraception will do so effectively. Emergency contraception is different from a medical abortion (an abortion induced by taking the prescription pills mifepristone and misoprostol) — and taking emergency contraception will not harm an existing pregnancy.

And the medical world is firm in its resolution that emergency contraception does not end a pregnancy. In 2014, Susan F. Wood (an Associate Professor at George Washington University and former director of the women's health office at the FDA) told The Daily Beast , “You don’t have a pregnant woman until the egg implants in a woman and sticks.” She went on to say: “That’s what the medical world has long considered pregnancy. That’s what the FDA thinks of as pregnancy. And that’s what our society thinks of as pregnancy.” So, medically, the claim that emergency contraception terminates an existing pregnancy is not accurate.

5. EC Has Some Potential Physical Side Effects

Emergency contraception does have some potential side effects. According to the National Institute of Health's U.S. National Library of Medicine, the most common ones are fatigue, headache, nausea and vomiting, and changes in menstrual bleeding.

Personally, when I took the drug, my side effects were minimal, and for me, they were worth it. I experienced some pretty bad breast pain and tenderness, but it went away after a couple of days. I also felt some aching in my abdomen. I felt a little off emotionally, too, which is not a documented side effect of EC — that could have just been because I was struggling with the state of my relationship at the time, though.

Like with all medications, you should be aware of how emergency contraception works, and how it can make you feel before you decide to take it. That said, emergency contraception is a viable option for preventing pregnancy. Obviously, practicing safe sex is your best option for staying healthy and preventing pregnancy — but people aren't infallible, and while emergency contraception won't keep you from contracting an STD, it is highly likely to keep you from becoming pregnant when you're not ready.

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