Here's What to Expect When You Take the Morning-After Pill



Education surrounding uterine sexual and reproductive health can get cloudy, and it's difficult to know who or what to believe. Such is the case with information regarding abortions, birth control, and emergency contraception. Personally, I grew up believing birth control solved every problem—skin concerns, heavy bleeding, unwanted pregnancy, irregular periods, and cramps. At least that's what was reported to us at 14, and all my friends began taking it. Now, we know otherwise. While birth control can help with many of those issues, it's more complicated than a magical cure-all.

The same goes for the morning-after pill. Although it can have side effects, Plan B is safe. But I was told emergency contraception would ravage my body and to be very cautious about taking it (and certainly not to take it too often). All of this just goes to show how much further we need to go to get to a place where people are given all the information and shame is no longer hurtled in our direction when we ask for it.

So I reached out to experts Michelle Metz, MD, and Zev Williams, MD, Ph.D., to break down exactly what we need to know: what Plan B does to our bodies when we take it, how many times you can take it, and what the side effects will be. Keep reading to find out everything you need to know about Plan B.

plan b
Grace Kim / Byrdie

What Is Plan B?

Plan B is an emergency contraceptive—not an abortion pill. Emergency contraception does come in different forms. However, most often, "the morning-after pill" refers to Plan B One-Step (and generics like Next Choice One Dose) that come with a single pill and can be purchased over the counter at the drugstore. "The Plan B pill is a form of emergency contraception that can either prevent or delay ovulation. It can also stop an egg from undergoing fertilization or prevent a fertilized egg from implanting in the uterine lining," explains Metz.

Meet the Expert

  • Michelle Metz, MD, is an assistant clinical professor in obstetrics, gynecology and reproductive science at Mount Sinai.
  • Zev Williams, MD, PhD, is the chief of the division of reproductive endocrinology and infertility at Columbia University Medical Center.

"It consists of a medication called levonorgestrel, which is similar to the hormone progesterone," adds Williams. "Ovulation, which refers to the release of an egg from the ovary, occurs when the brain releases a hormone, called luteinizing hormone. The LH travels through the blood from the brain to the ovary and signals the egg to be released," Williams says. Plan B prevents LH from being released and thereby prevents ovulation. No ovulation = no egg = no fertilization. Additionally, emergency contraception makes it much less likely you'll get pregnant but doesn't terminate an existing pregnancy.

(Side note: The actual abortion pill is made of a combination of mifepristone and misoprostol, which you can get access to at a doctor's office or Planned Parenthood and may be taken separately or together depending on the type. Acting in tandem, they stop the pregnancy from growing and cause your uterus to cramp and bleed, which leads to an abortion).

What Are the Side Effects of Plan B?

Some people experience nausea, vomiting, or headache, while others experience no side effects at all. "Breast tenderness (progesterone causes the milk glands to swell), bloating, mood swings (caused by hormonal fluctuation), sleepiness, and/or dizziness are common after taking emergency contraception," Williams says. "Another way to think about it is this: If a pregnancy occurs, progesterone is produced in the placenta and levels remain elevated throughout the pregnancy—so if you're taking a progesterone pill, you're getting all the symptoms of pregnancy," he adds.

Plan B can cause menstrual irregularities, making your next period come late or early, and it might be heavier and could last longer with more days of bleeding. "If your period doesn't come, the first thing you should do is take a pregnancy test," says Metz.

Is Plan B Safe?

"All the rumors you hear about [the morning-after pill] are completely untrue," says Charlotte Wilken-Jensen, head of the Gynecology and Obstetrics Department at Hvidovre Hospital in Denmark. "Every formula of the morning-after pill advises you to take it only once every cycle, but really, you can safely take it anytime you have unprotected intercourse. Of course, if you take it more than once, your risks of side effects increase." Essentially, taking the morning-after pill is akin to taking a bunch of birth control pills all at once. While you probably won't feel great, it won't negatively affect your health or fertility. "In the past, women who needed emergency contraception would just take a super-high dose of birth control, but the estrogen just caused a lot of nausea and vomiting," says Alyssa Dweck, a board-certified ob-gyn and author of The Complete A to Z for Your V. "It's very safe and well-tolerated, even in women who aren't able to take some birth control pills because of clotting disorders."

Can Weight Affect the Pill's Effectiveness?

Admittedly, I had no idea there were discussions around if one's weight skews the morning-after pill's effectiveness. It wasn't until a reader (shout out to Emily) wrote in to illuminate the issue that I saw any research on it whatsoever. A 2011 study found some evidence to support that a one's weight (specifically over 165 pounds) does affect the efficacy of the pill. That said, a 2017 study concluded BMI—which is not an indicator of health—had no such impact. The  The FDA issued a statement saying they have no plans to include a warning label on the package due to conflicting evidence and limited research. Still, it is important to be able to make informed decisions. The general consensus is that the morning after pill can be less effective for people with a BMI above 25. According to Ella and Copper, IUDs are two other forms of emergency contraception that are as effective across BMIs.

When Should You Take Plan B?

It's much more effective if you take it within 24 hours, but, according to Metz, you can take emergency contraception up to 72 hours after unprotected sex. "In order for the morning-after pill to work, it has to be taken before ovulation has occurred," continues Williams. After fertilization has happened, the morning-after pill won't prevent the embryo from developing, traveling through the fallopian tube, or implanting in the uterus. "Ella, an emergency contraceptive that requires a prescription, can be taken for up to five days following unprotected sex," instructs Williams.

The Final Takeaway

In general, Plan B is safe and well-tolerated. Plan B can cause changes in your period as well as nausea, vomiting, or headache; however, not everyone experiences side effects.

Article Sources
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  1. Glasier A, Cameron ST, Blithe D, et al. Can we identify women at risk of pregnancy despite using emergency contraception? data from randomized trials of ulipristal acetate and levonorgestrelContraception. 2011;84(4):363-367. doi:10.1016/j.contraception.2011.02.009

  2. Festin MPR, Peregoudov A, Seuc A, Kiarie J, Temmerman M. Effect of BMI and body weight on pregnancy rates with LNG as emergency contraception: analysis of four WHO HRP studiesContraception. 2017;95(1):50-54. doi:10.1016/j.contraception.2016.08.001

  3. Noé G, Croxatto HB, Salvatierra AM, et al. Contraceptive efficacy of emergency contraception with levonorgestrel given before or after ovulationContraception. 2010;81(5):414-420. doi:10.1016/j.contraception.2009.12.015

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