Which birth control is right for you? Take our quiz.
Back to Blog
How Plan B Affects Periods: What to Expect and When

How Plan B Affects Periods: What to Expect and When

  • Sonia Easaw, M.S., MPH
    Reviewed By: Shannon DeVita DNP, FNP-BC, CPNP-PC, Julie Lamonoff, CNM, OBGYN-NP

Plan B One-Step™, often just referred to as "Plan B," can be a superhero: It helps many women significantly lower their pregnancy risk after unprotected sex. It's safe to use, but just like birth control can affect your periods, so can Plan B. Here's how Plan B, also known as the morning-after pill or emergency contraception, can affect your menstrual cycle and for how long.

Can Plan B affect your period?

The short answer is yes: Plan B can affect your period because it can change your menstrual cycle's timing. The National Institutes of Health says that emergency contraception may cause mild side effects like menstrual bleeding changes. After taking Plan B, your next period may start earlier or later than you expect, and it could be heavier or lighter than usual. To understand why you have to know how emergency contraception works.

What is emergency contraception?

The Office on Women's Health says that the FDA first approved emergency contraceptive pills in 1998. The easiest way to explain Plan B is to compare it to its closest cousin: birth control pills.

Just like hormonal birth control, Plan B prevents a woman from getting pregnant after unprotected sex by:

  • Stopping the ovary from releasing an egg (a process called ovulation)
  • Blocking sperm from reaching the egg if it's already been released

Plan B just has a higher dose of hormones (e.g., the hormone levonorgestrel) than birth control pills. Doctors say it shouldn't be used as a regular form of birth control.

You might know Plan B as the "morning-after pill" that goes by a few names: Plan B One-Step, Take Action™, My Way™, ella™ and more.

Is Plan B the same as the abortion pill? It's crucial to note that Plan B is not an abortion pill. The American College of Obstetricians and Gynecologists says that emergency contraception only works before pregnancy officially begins. If the egg and sperm have already met, fertilized, and implanted into the uterus lining, it's pretty much a done deal. Just like hormonal birth control, it helps prevent pregnancy before it starts.

When researchers studied high-dose birth control pills, they found no risk to a developing embryo if the pregnancy had already begun. This means that if you still get pregnant even after Plan B, you don't have to worry that the actual Plan B medication would harm the pregnancy.

How can Plan B (morning-after pill) affect your period?

There are two types of emergency contraceptive pills (each with a different hormone), but you can expect these kinds of menstrual changes to happen after taking either of them:

  • An early or late period after taking the pill
  • Changes to your next period (the one you'd expect to come after your current cycle)

Researchers at Princeton University looked at past studies and said that menstrual cycles could be shortened after taking Plan B, meaning that the time between now and when you get your next period could be shorter. When we talk menstrual cycles, we're tracking the first day you get your period as day 1, up until the first day of your next period. Everyone's different, but usually, you'd get your period every 28 days or so.

They also found even if Plan B didn't shorten the time until your next cycle, it could cause your next period the following month to be longer.

Types of emergency contraception pills

There are 2 types of emergency contraceptive pills commonly sold in the U.S.:

  1. Plan B One-Step™ (also sold under names like Next Choice™ or AfterPill™) - to be taken as soon as possible and within 72 hours of unprotected sex
  2. ella™ - to be taken as quickly as possible after unprotected sex and within 5 days

Editor's note: Technically, a doctor could have you take higher doses of regular combination birth control pills as emergency contraception, something called the Yuzpe regimen. But that's not as effective as the other 2 types listed above, and it brings with it more side effects. Additionally, the copper IUD could be inserted within 5 days as a form of emergency contraception.

Scientists have found that both Plan B One-Step™ (or equivalent generics) that you can get over-the-counter, or the prescription for ella™, are safe to use to prevent pregnancy. Any side effects that you have after taking either of the emergency contraceptive pills should be mild and short-term.

After you take emergency contraceptive pills, the most common side effect is - you guessed it - changes to your menstrual periods.

Here is a list of some possible side effects after using a "morning-after" pill like Plan B:

  • Irregular bleeding
  • Nausea
  • Headaches
  • Breast tenderness
  • Abdominal pain
  • Dizziness
  • Fatigue

Plan B One-Step and menstrual changes

If you take Plan B One-Step or one of its brand-name equivalents, you're essentially taking a pill that has the hormone levonorgestrel, a type of progestin. This hormone is what's going to help delay the release of the egg and some other more complicated functions.

Scientists have found that changes to your period after taking Plan B depend on when in your menstrual cycle you took it. After all, all things pregnancy-related depend on your cycle! They found that depending on where you were in your cycle when you took Plan B, your next period could come early or late. One study showed that, on average, when you take Plan B, your period could start 1 day earlier.

By prescription-only: ella™ and menstrual changes

The FDA approved the emergency contraceptive ella in 2015. It's the most effective emergency contraceptive pill in the U.S. Its star ingredient is the chemical ulipristal acetate. Like its rival levonorgestrel in Plan B, ulipristal acetate works primarily by delaying ovulation. Researchers have found that one side effect of taking ella could be your period is delayed by about 2 days.

How do you know if Plan B worked?

Doctors say that you don't need any tests or procedures after using emergency contraception. However, if you haven't gotten your period within a week of when it should come or expect it to come, you should have a pregnancy test. Don't hesitate to talk to your doctor for some good, solid medical advice.

When you take it as directed, your emergency contraception pill should be safe and effective. The California State Board of Pharmacy says that emergency contraception could reduce your risk of getting pregnant by up to 89%. Note that this number is only an estimate, and it rides upon the fact that you take it on time, as soon as possible after having unprotected sex.

Takeaways: Can Plan B affect your period?

The number one side effect of taking Plan B is irregular periods, which can come early or be delayed by a couple of days. Taking emergency contraception could also affect your next month's period. But the effects usually resolve on their own, and no treatment is necessary. If you don't get your period within a week of when you expect it to come, however, it's probably a good idea to get a pregnancy test or get medical advice.

It's important to know that accidents happen - a condom could break, you might forget to take your birth control pills for a few days, etc. It's a great "last-chance" option that public health professionals say is not used often enough. Though you can get Plan B at most local drugstores and pharmacies, it may not be accessible for everyone. That's why it's good to be prepared: Online birth control delivery companies like ours, The Pill Club, can send Plan B with your package, so you have it when you need it.

Emergency contraception is a lifesaver to many. It's a temporary fix, though. Make sure to continue to use your regular birth control method, like birth control pills or condoms, every time you have sex.


Birth control
Get birth control delivered for free, with goodies!

Give yourself the gift of birth control auto-refills, plus free delivery and self care samples in every package.

Join Now