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Drug Info

Plan B One-Step side effects

The most common Plan B side effects are changes in the menstrual cycle and heavy periods, but other minor side effects have been reported
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By | Dec. 1, 2023 Medically reviewed by Karen Berger, Pharm.D.
A clock and birth control pills: Plan B side effects

Key takeaways

  • Plan B One-Step is an emergency contraceptive that is most effective when taken within 72 hours after unprotected sex, but it is not an abortion pill and does not affect long-term fertility.

  • Common side effects include changes in the menstrual cycle, nausea, lower abdominal pain, fatigue, dizziness, and headaches, with menstrual changes being the most reported.

  • Serious side effects from Plan B are rare, and the medication does not have significant interactions with other drugs, but certain medications may reduce its effectiveness.

  • Plan B is considered safe for women and adolescents who have had their first period, with no severe side effects or long-term health risks associated with its use.

In this article:

Plan B One-Step is a brand-name version of the generic drug used for emergency birth control after a woman has unprotected intercourse or other forms of contraception fail. Plan B One-Step is available without a prescription from pharmacies and retailers that sell over-the-counter (OTC) medication. A single Plan B One-Step tablet must be taken as soon as possible after the sexual encounter to prevent pregnancy. It is most effective within 72 hours, but it may still work if taken within five days. The sooner the tablet is taken, the more effective it will be in preventing pregnancy. Plan B One-Step is an emergency birth control pill, not a routine birth control pill, and not an abortion pill. The Plan B pill temporarily delays ovulation if it hasn’t already occurred. It won’t work if you have already started ovulating. 

Common side effects of Plan B

According to a review of 11 studies of emergency contraception, menstrual changes are the most common side effect of using emergency birth control pills like Plan B. That’s because Plan B temporarily delays ovulation, affecting the rest of the menstrual cycle.

Plan B prescribing information shared by the Food and Drug Administration (FDA) lists heavier menstrual bleeding (31%), nausea (14%), lower abdominal pain (13%), fatigue (13%), dizziness (10%), and headache (10%) as the most commonly reported side effects in original clinical trials of Plan B.

Other reported side effects of taking a single Plan B One-Step tablet include:

  • Periods that are early, late, heavier, or lighter than normal
  • Abnormal spotting or bleeding
  • Breast tenderness
  • Vomiting
  • Pelvic pain

Serious side effects of Plan B

Clinical studies have shown that Plan B is well-tolerated and not expected to cause serious side effects.

Plan B’s effect on mood and emotions

Although mood changes are not listed on FDA prescribing information as a side effect of Plan B One-Step, some women have reported mood swings and negative emotions after taking it. Although one study by the University of Pennsylvania found no psychological effects in 120 women in the two weeks following the use of emergency contraception, it was conducted in 1979. More research is needed on the effects of emergency contraception like Plan B on mood, but recent studies haven’t found a connection between mood swings and routine (not emergency) oral contraception overall, according to the MGH Center for Women’s Mental Health. 

That doesn’t mean mood swings or bad emotions aren’t a possible side effect. Some people can have unique responses to drugs that other people don’t have.

Plan B and bleeding

The most common side effect of Plan B One-Step is changes in menstruation. The Plan B fact sheet shared by the drug manufacturer lists early periods, late periods, light periods, and heavy periods as side effects. Research has shown that the impact on the menstrual cycle depends on when the pill is taken. When taken early in the cycle, the menstrual cycle may be shortened. When taken later in the cycle, the cycle is typically either unchanged or lengthened. Bleeding, however, is likely to be experienced as either a heavy menstrual period or unusual spotting. In the original clinical trials of Plan B, almost 31% of participants reported bleeding as a side effect.

Plan B and nausea

Nausea is a common side effect of levonorgestrel emergency contraception. Vomiting is less common. However, if a woman vomits within two hours of taking Plan B, she should call her healthcare provider and ask about taking a second Plan B pill.

How soon do Plan B side effects start?

The most common side effects of Plan B, changes in the menstrual cycle and heavier bleeding, will not be noticed until days or weeks after taking the pill. Other side effects happen early and are only temporary. 

How long do Plan B side effects last?

Plan B side effects are limited to a single menstrual cycle. Most side effects pass in a few days as hormone levels return to normal. Menstrual changes such as spotting or menstrual cycle irregularities won’t occur until days or weeks later. Those changes should affect only one menstrual cycle.

What are the long-term side effects of Plan B?

There are no long-term side effects associated with Plan B. Plan B does not affect a woman’s long-term ability to get pregnant. Long-term monthly use of Plan B has not been studied, but there are no reports of adverse effects from regular monthly use of levonorgestrel emergency contraception. Although you can use Plan B as often as you need to, it should not be used as your regular birth control. You can always consult your healthcare provider to help you find the best type of birth control that fits your needs and lifestyle.

Plan B interactions

Plan B is not more likely to cause side effects when combined with other drugs. However, some drugs may speed up the body’s metabolism of levonorgestrel. When those drugs are taken along with Plan B, the Plan B pill may not work as well, and there’s a higher risk of pregnancy, according to its prescribing information. Those drugs include:

Women who are taking daily hormonal birth control pills can take Plan B without additional adverse effects. In fact, women who miss at least three doses of daily birth control pills are advised to use emergency contraception after having unprotected sex.

Safety measures while using Plan B

Boxed warning

The FDA mandates boxed (or black box) warnings for drugs that have a significant risk of severe side effects. As a nonprescription drug, Plan B does not have risks that merit a black box warning.

Precautions

Plan B One-Step is contraindicated (should not be used) by people who have had allergic reactions to levonorgestrel.

Plan B should not be taken by women who are pregnant, past menopause, or who haven’t had their first period. Plan B should also not be taken by people assigned male at birth. Plan B One-Step should not be used as a regular form of birth control.

Plan B doesn’t have any dosage restrictions or precautions for people with pre-existing medical conditions, including kidney disease and liver disease. There are no specified dosage adjustments based on body weight. Plan B One-Step is effective in women with higher BMIs.

Plan B One-Step cannot prevent sexually transmitted infections (STIs) such as HIV or AIDS.

Children

Plan B is safe to use in female adolescents and children who have had their first period. On June 20, 2013, the FDA approved Plan B One-Step for nonprescription use without any age restrictions.

Pregnancy

Plan B should not be taken by women who are pregnant. There is no medical reason for it, and the drug will not terminate an existing pregnancy. According to the FDA drug information, taking Plan B during a pregnancy will not cause birth defects or other problems in the fetus. However, the effects of levonorgestrel emergency contraception on pregnant women have not been studied to see if it can cause pregnancy problems like preterm delivery or low birth weight.

Breastfeeding

Plan B can be taken by women who are breastfeeding. Side effects in a nursing infant are not expected when the mother takes a progestin-only drug like Plan B. Women who are breastfeeding can nurse a baby three to four hours after taking Plan B.

Dependence

Levonorgestrel is not a controlled substance and does not cause dependence or withdrawal symptoms.

Overdose

Plan B One-Step is sold as a single tablet at an average retail price of $47. Even if a person takes too many Plan B One-Step tablets, an overdose is not considered dangerous. Although taking too many Plan B tablets may increase the likelihood of possible side effects such as nausea, vomiting, and lower abdominal pain, there are no severe side effects associated with an overdose. Still, if too many Plan B One-Step pills are taken, call at 1-800-222-1222 or get medical help as soon as possible.

Recalls

Plan B One-Step has no history of recalls. 

How to avoid Plan B side effects

Plan B side effects are generally mild. Many can’t be avoided, but they can be partly avoided or minimized by following a few pointers:

  • Take Plan B as instructed. Read the package insert carefully and follow the directions. Plan B can be taken with or without food. This will not change its effectiveness or possible side effects. 
  • Talk to a healthcare professional if you vomit shortly after taking Plan B. Vomiting is rare but a possible side effect of Plan B. If you vomit within two hours of taking Plan B, you may have vomited out the medicine. Before taking another pill, call a healthcare provider for medical advice.
  • Avoid taking Plan B several times in a month, if possible. Plan B can be safely taken more than once per month as emergency contraception. However, sexually active women should not use Plan B One-Step as their only means of birth control, taking it each time they’re at risk of getting pregnant. Instead, ask a healthcare provider or visit a gynecologist, women’s health clinic, reproductive health clinic, or Planned Parenthood for other forms of birth control, such as birth control pills or an intrauterine device (IUD).
  • Eat something after taking the Plan B pill. Plan B may cause nausea, so it may help to eat something when taking the pill to stave off or minimize nausea.
  • Do not take Plan B with Ella. Plan B (levonorgestrel) is just one type of morning-after pill. Women can also take ulipristal acetate, sold under the brand name Ella, which is a prescription drug. To ensure the effectiveness of ulipristal, healthcare professionals advise women not to take a levonorgestrel emergency contraception pill (such as Plan B) within five days of having taken Ella.
  • Take a pregnancy test if your next period is more than seven days late. Plan B can delay your next period. However, if your next period is delayed for seven days or longer, that’s a possible sign of pregnancy. Taking another Plan B pill will not terminate an existing pregnancy.

How to treat side effects of Plan B

Not all side effects of Plan B are treatable. Menstruation changes cannot be avoided or treated. Other potential side effects are mild, and most can be managed:

  • Nausea and stomach pain: Nausea and stomach pain can be improved with OTC remedies such as Pepto-Bismol or Kaopectate. You can also eat foods that are less irritating, such as crackers, dry toast, rice, bananas, and applesauce, and drink soothing beverages like water, tea, or ginger ale.
  • Headache: OTC pain relievers like acetaminophen or ibuprofen should be sufficient to relieve headache pain after a dose of Plan B. You can also try resting in a cool, dark, quiet room—and drink plenty of fluids to stay hydrated.
  • Dizziness: There’s little to do about dizziness other than to wait it out—sit down, take it easy, and avoid driving and operating machinery until you feel better.
  • Breast tenderness: For a temporary period of breast tenderness or pain, immediate home treatments include hot or cold compresses or, in more severe cases, OTC pain relievers.
  • Severe lower abdominal pain: Get immediate medical care when experiencing severe lower abdominal pain in the weeks following Plan B use—severe abdominal pain is not considered a Plan B side effect but may be due to an ectopic pregnancy.

Bottom line: Is Plan B safe?

The FDA considers Plan B to be safe enough to be used without a prescription by women and adolescents who have had their first period. Many women will experience some side effects, but they’re mild and not health-threatening. There are no known severe side effects and no drug interactions that increase the risk of side effects. Taking too many Plan B pills will not cause serious problems. If you do not take a regular form of birth control, talk to your healthcare provider about the best type of birth control for you.

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