What should I do if I took Plan B (levonorgestrel) and missed my menstruation?

Management of Missed Menstruation After Taking Plan B (Levonorgestrel)

A pregnancy test should be performed if you miss your period after taking Plan B (levonorgestrel), as this is the most important first step to determine if the emergency contraception was effective. 1, 2

Initial Assessment

• Perform a pregnancy test first to rule out pregnancy, which is the most common concern after missed menstruation following Plan B use 1
• Plan B works by preventing or delaying ovulation and is approximately 85% effective when taken within 72 hours of unprotected intercourse 3, 2
• Menstrual changes are a common side effect of levonorgestrel emergency contraception and can include early, late, heavier, or lighter periods 2

Understanding Plan B's Effects on Menstruation

• Plan B may alter your menstrual cycle timing, with your next period potentially coming earlier or later than expected 2
• You will know Plan B has been effective when you get your next period, which should come at the expected time or within a week of the expected time 2
• If your period is delayed beyond 1 week after the expected time, pregnancy is possible and should be ruled out with a test 2

When to Seek Medical Attention

• If your period is more than a week late after taking Plan B, perform a pregnancy test 2
• Seek immediate medical attention if you experience severe abdominal pain, as this could indicate an ectopic pregnancy 2
• Contact a healthcare provider if you vomited within 2 hours of taking Plan B, as you may need to repeat the dose 2

Follow-up Recommendations

• If pregnancy test is negative and period is still absent:

  • Wait another week and retest if period doesn't return 1
  • Consider evaluation for other causes of amenorrhea if period remains absent for more than 6 weeks 1

• If pregnancy test is positive:

  • Schedule an appointment with a healthcare provider for prenatal care 1
  • Be aware that Plan B will not affect an existing pregnancy 2

Important Considerations

• Plan B is not intended for regular contraception and is less effective than regular birth control methods 2
• Consider discussing more reliable long-term contraceptive options with your healthcare provider 3
• Remember that Plan B does not protect against sexually transmitted infections 2

Common Side Effects of Plan B

• Besides menstrual changes, other common side effects include nausea, lower abdominal pain, tiredness, headache, dizziness, and breast tenderness 2
• These side effects are typically mild and resolve on their own within a few days 2
• The effectiveness of Plan B may be reduced if you are taking certain medications including efavirenz (HIV medication), rifampin (tuberculosis treatment), or medications for seizures 2

Remember that while Plan B is effective emergency contraception, it should not replace regular contraceptive methods, which are more reliable for ongoing pregnancy prevention 2, 4.