What are the side effects of Plan B (levonorgestrel)?

Side Effects of Plan B (Levonorgestrel)

Plan B (levonorgestrel) emergency contraception commonly causes menstrual changes, nausea, headache, breast tenderness, fatigue, dizziness, and lower abdominal pain, but these side effects are generally mild and well-tolerated. 1, 2

Common Side Effects

Levonorgestrel emergency contraception typically causes the following side effects:

• Menstrual changes: The most common side effect is alteration in menstrual bleeding pattern, which may include:

  • Early or late menstruation (up to 1 week late in 21% of users) 3
  • Changes in flow (heavier or lighter periods) 2
  • Spotting or unscheduled bleeding 1, 3

• Gastrointestinal symptoms:

  • Nausea 1, 2, 4
  • Vomiting (less common than with combined estrogen-progestin ECPs) 1, 3

• Other common side effects:

  • Headache 2, 3
  • Lower abdominal pain 2, 3
  • Breast tenderness 2, 3
  • Fatigue/tiredness 2
  • Dizziness 2, 3

Frequency and Severity

• Most side effects are mild and transient, resolving within 24-48 hours 4
• Levonorgestrel causes significantly less nausea and vomiting than combined estrogen-progestin emergency contraceptive pills 1
• The prevalence of side effects is similar between the single 1.5mg dose and the two-dose 0.75mg regimen 4, 5

Uncommon Side Effects

Less frequently reported side effects include:

• Anorexia 4
• Weight changes 4
• Skin changes (exanthema, chloasma) 4

Important Clinical Considerations

Vomiting After Taking Plan B

• If vomiting occurs within 3 hours of taking Plan B, another dose should be taken as soon as possible 1
• Consider use of an antiemetic if vomiting is a concern 1

Pregnancy Concerns

• Plan B will not affect an existing pregnancy and is not effective if the woman is already pregnant 2
• Plan B is estimated to be up to 85% effective in preventing pregnancy when taken as directed 1, 2
• The effectiveness decreases the longer the delay between unprotected intercourse and taking the medication 2, 5
• Plan B may be less effective in women who weigh more than 165 pounds and potentially ineffective in women who weigh more than 176 pounds 1, 6

Follow-up Recommendations

• A woman should get her period at the expected time or within a week of the expected time 2
• If her period is delayed by more than a week, she should take a pregnancy test 2
• If she experiences severe abdominal pain, she should seek immediate medical attention as this could indicate an ectopic pregnancy 2

Important Caveats

1. Plan B should not be used as a regular contraceptive method as it is less effective than other contraceptive options 2, 7

2. Plan B does not protect against sexually transmitted infections (STIs) 2

3. Plan B should be taken as soon as possible after unprotected intercourse for maximum effectiveness, though it can be taken up to 72-120 hours afterward 6, 2

4. Women taking certain medications (efavirenz for HIV, rifampin for tuberculosis, or seizure medications) should consult a healthcare provider as these may reduce the effectiveness of Plan B 2