How does the body feel after taking Plan B? A comprehensive guide to expected side effects

October 10, 2025 •

4 min read

Emergency contraceptive pills like Plan B contain a high dose of the hormone levonorgestrel, which can cause temporary, noticeable side effects in many people. Understanding how does the body feel after taking Plan B can help you anticipate and manage these common reactions.

Quick Summary

Plan B introduces a temporary, concentrated surge of hormones that can cause short-term side effects like nausea, fatigue, and headaches. Many women also experience temporary changes to their next menstrual cycle, with most symptoms resolving within a few days.

Key Points

Immediate Side Effects: Nausea, headaches, fatigue, and dizziness can occur within hours or a day of taking Plan B due to the high hormone dose.
Menstrual Cycle Changes: Your next period may be earlier, later, heavier, or lighter than usual, and spotting is common between cycles.
Temporary Discomfort: Breast tenderness and mild abdominal cramping are normal and typically linked to the hormonal shift, resolving within a few days.
Monitor for Concerns: While rare, severe abdominal pain or heavy, prolonged bleeding requires immediate medical attention as it could signal a serious issue.
Not for Regular Use: Plan B is a safe and effective emergency contraceptive, but it is not intended for use as a regular form of birth control.
Mood Swings: Some users report emotional fluctuations, like mood swings or depression, although this is not a universally listed side effect.

Plan B, the popular brand name for a levonorgestrel emergency contraceptive pill, is a safe and effective method to prevent pregnancy after unprotected sex or contraceptive failure. It works by delivering a high dose of the synthetic hormone levonorgestrel, which delays or prevents ovulation. This concentrated hormonal surge can lead to a variety of temporary side effects as your body adjusts. Most side effects are mild and resolve within a few days, but being prepared can help you manage your experience and reduce anxiety.

Immediate and Short-Term Physical Side Effects

Many of the initial reactions to Plan B are caused by the sudden shift in hormone levels. They can start within a few hours of taking the pill and generally subside quickly.

Nausea and Vomiting

Nausea is one of the most frequently reported side effects of taking Plan B. It can range from a mild, queasy feeling to an upset stomach. Vomiting is less common but can occur.

Management tip: Eating a small meal or a snack before taking the pill can help reduce nausea. Consider taking an over-the-counter anti-nausea medication about an hour beforehand if you are prone to motion sickness or have a sensitive stomach.
Important note: If you vomit within two hours of taking Plan B, the medication may not have been fully absorbed. You should contact a pharmacist or healthcare provider to determine if you need to take another dose.

Headache and Dizziness

A mild headache or a feeling of lightheadedness or dizziness is also common. These symptoms are typically short-lived.

Management tip: Rest in a quiet place and stay hydrated. Over-the-counter pain relievers, like ibuprofen or acetaminophen, are safe to use with Plan B if needed.

Fatigue and Tiredness

It is not unusual to feel a bit more tired than usual after taking Plan B. This fatigue is a normal response to the hormonal changes and should pass within a day or two.

Breast Tenderness

Breast tenderness or soreness can occur due to the high dose of progesterone-mimicking hormones in the pill. For some, this feels similar to the tenderness experienced before a regular period.

Management tip: Warm compresses or a warm bath may help soothe discomfort. Wearing a supportive bra can also provide relief.

Abdominal Pain and Cramping

Lower abdominal pain or cramping, similar to menstrual cramps, can be a short-term side effect. These are typically mild and not a cause for concern.

Management tip: A heating pad or over-the-counter pain relievers can help ease the discomfort.

Menstrual Cycle Changes and Spotting

Plan B's effect on your hormonal balance can significantly impact your next menstrual cycle. While these changes are temporary, they can be confusing or cause anxiety if you are not prepared for them.

Change in timing: Your next period may arrive earlier or later than expected, sometimes by up to a week. If your period is more than a week late, you should take a pregnancy test.
Change in flow: The flow of your next period might be heavier or lighter than your usual period.
Spotting: Light bleeding or spotting between taking the pill and your next period is a common side effect. This is not your period but rather a result of the hormonal shift.

Emotional and Mood-Related Side Effects

While not officially listed as a side effect by the FDA in all materials, some women have reported experiencing mood changes, mood swings, or feelings of depression after taking Plan B. The high concentration of synthetic hormones can affect an individual's emotional state, and every person's response is unique.

Comparison Table: Common Plan B Side Effects


Side Effect	Description	Typical Duration	Management Tips
Nausea	Feeling queasy or upset stomach.	1-2 days	Take with food, use anti-nausea medication.
Headache/Dizziness	Mild head pain or feeling lightheaded.	1-2 days	Rest, stay hydrated, use OTC pain reliever.
Fatigue	Feeling unusually tired or drained.	1-2 days	Get extra rest, prioritize sleep.
Breast Tenderness	Sore or sensitive breasts.	1-2 days	Wear a supportive bra, use warm compresses.
Abdominal Cramping	Mild pain similar to menstrual cramps.	1-2 days	Use a heating pad, use OTC pain reliever.
Menstrual Cycle Changes	Next period is early, late, or has a different flow.	1 cycle	Take a pregnancy test if period is over a week late.
Spotting	Light bleeding between periods.	A few days	Wait for your next regular period.

When to Seek Medical Attention

While most side effects are mild, some symptoms warrant contacting a healthcare provider:

Severe lower abdominal pain, especially if it occurs three to five weeks after taking the pill. This could be a sign of an ectopic pregnancy, a medical emergency.
Heavy, prolonged bleeding (e.g., soaking through multiple pads/tampons per hour for several hours).
Your next period is more than a week late.
Signs of a severe allergic reaction, such as hives, difficulty breathing, or swelling of the face, tongue, or throat.

Conclusion

For most individuals, the side effects of taking Plan B are temporary and manageable, primarily stemming from the large dose of synthetic hormones. Physical symptoms like nausea, fatigue, and breast tenderness typically subside within a couple of days. Changes to the menstrual cycle, including the timing and flow of your next period, are also common but temporary. By understanding and anticipating these possible reactions, you can navigate the experience with greater confidence. Remember that while Plan B is a safe and effective emergency contraceptive, it is not a substitute for regular birth control. For ongoing, reliable protection, speak with a healthcare provider about other contraceptive options.

Here is an authoritative link for further reading on emergency contraception from Planned Parenthood.

Frequently Asked Questions

Most immediate side effects like nausea, headache, and fatigue typically resolve within one to two days. Menstrual cycle changes, such as a delayed or altered period, will be noticeable around the time of your next cycle, but usually normalize afterward.

If you vomit within two hours of taking the pill, it may not have been absorbed effectively. You should contact a healthcare provider or pharmacist, as another dose may be necessary.

Yes, Plan B can cause your next period to be delayed, sometimes by up to a week. If your period is more than a week late, it is recommended to take a pregnancy test.

Not necessarily. Spotting or light bleeding is a common side effect caused by hormonal changes. It is not a definitive sign that the pill was effective. A pregnancy test is the only way to be sure if your period is late.

Some individuals report experiencing mood swings or emotional changes after taking Plan B, though this is not a universally recognized side effect. This is believed to be a reaction to the high dose of hormones.

To help manage nausea, try eating a small snack before taking the pill. You can also take an over-the-counter anti-nausea medication about an hour beforehand.

You should seek medical attention if you experience severe lower abdominal pain, heavy or prolonged vaginal bleeding, or if your period is more than a week late. These could be signs of a serious health issue, like an ectopic pregnancy.