9 Plan B Side Effects You Should Know About

Emergency contraception is one of the many forms of birth control available. It’s taken shortly after having sex when a primary birth control method failed or wasn’t used. For example, a condom broke during sex or a birth control patch fell off without you realizing it.

Plan B (the morning after pill) is one of the most well-known and accessible emergency contraceptives available. While not free of side effects, it’s generally well tolerated. Below, we’ll review the basics of Plan B, including nine side effects you should be aware of.

What is Plan B and how does it work?

Plan B One-Step (levonorgestrel) is a single-dose oral emergency contraceptive pill. It’s available over-the-counter (OTC) and can be purchased by anyone of any age. It’s about 89% effective when taken within 72 hours (3 days) of unprotected sex.

Plan B works by temporarily delaying ovulation (the release of an egg). This can prevent sperm from fertilizing an egg. And a pregnancy can’t happen without a fertilized egg.

Because of how it works, Plan B likely isn’t effective if you’ve already ovulated. But your chance of pregnancy is also much lower if it’s been more than 24 hours since ovulation — with or without Plan B.

Keep in mind that most people don’t know when they ovulate. And, it’s not harmful to take Plan B during this part of your menstrual cycle. So it’s a good idea to take Plan B after unprotected sex — even if you may have already ovulated.

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Good to know: Plan B is not a form of abortion. It won’t stop a pregnancy that’s already begun. And it doesn’t affect future fertility.

Side effects of Plan B

Because Plan B is very accessible, you may purchase it without even thinking about potential side effects. But all medications, including OTC products, have risks.

Common Plan B side effects include:

• Heavier period the next time

• Spotting or breakthrough bleeding

• Nausea or vomiting

• Lower abdominal (stomach) pain

• Tiredness

• Headache

• Dizziness

• Breast tenderness

• Late period the next time

Plan B side effects are typically mild and should resolve on their own. Serious side effects weren’t reported during clinical trials. So if you experience anything severe, contact your healthcare provider. Below, we’ll detail these nine Plan B side effects and provide tips for managing them.

Note: Information on Plan B’s side effects is based on clinical studies from the original prescription-only version.

1. Heavier period the next time

Having a heavier period the next time is the most common side effect of Plan B. About 1 in every 3 women reported this during clinical trials. This shouldn’t be dangerous and should only affect your next period. But it can be annoying.

Let your healthcare provider know if you’re soaking through a full tampon or sanitary pad every hour for more than 2 to 3 hours. You should also contact them if you’re passing large clots. These are symptoms of abnormal uterine bleeding and should be checked out by a provider.

2. Spotting or breakthrough bleeding

Spotting and breakthrough bleeding are also possible Plan B side effects. If you experience this, it would likely happen a few days after taking the medication. Similar to a heavier period, this shouldn’t be harmful.

You may want to use panty liners or opt to wear darker-colored underwear after taking Plan B. If you’re still experiencing spotting or breakthrough bleeding after your next period is over, contact your healthcare provider. There may be anothe

3. Nausea or vomiting

Nausea is also common with Plan B. No one likes that feeling of having to throw up. Taking your dose with food can help lessen or prevent this side effect. Some people also find that sipping ginger or peppermint tea helps calm an upset stomach.

Vomiting is less common with Plan B, but possible. If you throw up within 2 hours of taking Plan B, contact your healthcare provider or pharmacist. You may need to take another dose.

4. Lower abdominal pain

Lower abdominal pain after taking Plan B happens about as often as nausea. This could feel similar to menstrual cramp pain. This is generally mild and should pass quickly. Until it lets up, stay well hydrated and avoid foods that can irritate your stomach, like spicy or high-fat foods.

You can also take an OTC pain reliever, such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin). Neither interact with Plan B. Let your provider know if abdominal pain persists or is severe.

5. Tiredness

Feeling tired after taking Plan B is also pretty common. As with the side effects above, this shouldn’t be severe. It may feel similar to fatigue you might experience during your periods. Be kind to your body and take it easy if you feel fatigued. It’s usually temporary and should go away on its own.

6. Headache

Headache is a common side effect for many medications. And Plan B is no exception. Headache is estimated to happen to about 10% of those who take Plan B.

Getting extra rest and avoiding loud noises may help ease headaches. OTC pain relievers can also be helpful for managing this Plan B side effect.

7. Dizziness

While less common than the side effects already mentioned, dizziness can happen after taking Plan B. It’s possible you could experience this along with other side effects, like nausea or headache. Just keep in mind that it should get better relatively quickly. Try to sit or lie down if you feel dizzy. And take care to change positions slowly to help prevent falls.

7. Breast tenderness

Breast pain or discomfort is a common side effect of many birth control methods. That’s because some people are more sensitive to hormones than others. If this happens to you, dress comfortably and avoid tight fitting items around your chest area until the side effect passes. OTC pain relievers, such as ibuprofen, can also be helpful.

8. Late period the next time

A late period can be a very worrying Plan B side effect. But it happens because of how the medication works.

Typically there’s about 14 days between when you ovulate and when you get your period. Because Plan B can delay ovulation by a few days, that 14-day countdown will also start later.

Typically, Plan B doesn’t delay your next period by more than a week. A period this late is less common. If you don’t get your period within 21 days of taking Plan B, you should take a pregnancy test or follow up with your healthcare provider.

How long do Plan B side effects last?

Many Plan B side effects — particularly headache and stomach-related side effects — should go away within 1 to 2 days. But side effects related to your menstrual period may not appear for a few days or weeks.

Here’s when you’d likely experience the Plan B side effects discussed above:

• Heavier period: During your next period, but shouldn’t affect any periods after that

• Spotting: A few days after you take Plan B

• Nausea: Within a few hours after taking Plan B (should resolve within a day or two)

• Abdominal pain: Within a few hours after taking Plan B (should resolve within a day or two)

• Tiredness: Within a few hours after taking Plan B (should resolve within a day or two)

• Headache: Within a few hours after taking Plan B (should resolve within a day or two)

• Dizziness: Within a few hours after taking Plan B (should resolve within a day or two)

• Breast tenderness: Within a few hours after taking Plan B (should resolve within a day or two)

• Late period: During your next period, but shouldn’t affect any periods after that

Plan B isn’t known to have any long-term side effects. If you’re still having symptoms after the timeframes mentioned above, contact your healthcare provider.

Good to know: Experiencing side effects from Plan B isn’t a reliable way to know if the medication definitely prevented a pregnancy. Keep in mind that many side effects listed in this article — such as nausea, tiredness, and breast tenderness — are also early pregnancy symptoms. The only way to know if Plan B was effective is if you get your next period.

When should I contact my healthcare provider about side effects from Plan B?

As discussed, Plan B side effects shouldn't be severe. If you’re experiencing any side effects that are greatly interfering with your daily routine or aren’t going away, contact your healthcare provider.

This is especially important if you experience unusual vaginal bleeding or severe stomach or pelvic pain during the weeks that follow taking Plan B. In very rare cases, people have experienced ectopic pregnancies after using emergency contraception.

An ectopic pregnancy is a pregnancy that happens outside of the uterus. It’s a medical emergency and can be life-threatening. Severe stomach or pelvic pain can be a warning sign of this condition. Seek emergency medical care if you believe you’re experiencing an ectopic pregnancy.

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Written by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

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