What is the most effective emergency contraception within 72 hours of unprotected sex?

Most Effective Emergency Contraception Within 72 Hours of Unprotected Sex

The copper intrauterine device (IUD) is the most effective emergency contraception method within 72 hours of unprotected sex, with an effectiveness rate of >99%. 1

Effectiveness Hierarchy of Emergency Contraception Options

1. Copper IUD (>99% effective) 1

   • Most effective option
   • Can be inserted up to 7 days after unprotected intercourse 2
   • Provides long-term contraception
   • Requires a healthcare provider for insertion

2. Ulipristal acetate (85% effective) 1, 3

   • Single 30mg oral dose
   • FDA-approved for use up to 120 hours (5 days) after unprotected sex
   • Prescription required
   • More effective than levonorgestrel, especially when taken later
   • Clinical trials showed pregnancy rate of 1.9% when taken within 72 hours 3

3. Levonorgestrel (75-80% effective) 1, 4

   • Single 1.5mg oral dose
   • FDA-approved for use up to 72 hours (3 days) after unprotected sex
   • Available over-the-counter
   • Clinical trials showed pregnancy rate of 2.6% when taken within 72 hours 5

Timing Considerations

• Critical factor: The sooner emergency contraception is taken, the more effective it will be 1, 4
• Effectiveness decreases with time for all methods 1, 4
• In direct comparison studies, ulipristal acetate showed superior efficacy to levonorgestrel, particularly when taken closer to the 72-hour mark 5
• A meta-analysis showed ulipristal acetate had significantly lower pregnancy rates (1.4%) compared to levonorgestrel (2.2%) when taken within 72 hours (p=0.046) 5

Special Population Considerations

• Higher BMI patients: Ulipristal acetate is preferred for patients with higher BMI as it maintains better efficacy in this population 1
• Medication interactions:
  • Efficacy of hormonal methods may be reduced when used with anticonvulsants, antimicrobials, HIV protease inhibitors, or St. John's wort 1
  • Patients taking efavirenz (HIV medication), rifampin (TB treatment), or seizure medications should consult a healthcare provider as these may reduce effectiveness of levonorgestrel 4

Common Side Effects

• Ulipristal acetate: Headache (19.3%), nausea, abdominal pain 5
• Levonorgestrel: Headache (18.9%), nausea, changes in menstrual cycle, lower abdominal pain, fatigue, dizziness, breast tenderness 4

Important Clinical Pearls

• A negative pregnancy test should be confirmed before administering emergency contraception 3
• Emergency contraception should not be used as regular birth control as it's less effective than ongoing contraceptive methods 4, 2
• If vomiting occurs within 2 hours of taking oral emergency contraception, the dose may need to be repeated 4
• Follow-up is recommended 5-7 days after expected onset of next menses 3
• The copper IUD has the added benefit of providing long-term contraception after emergency use 2

Remember that emergency contraception prevents pregnancy by stopping or delaying ovulation and will not terminate an existing pregnancy or protect against sexually transmitted infections 4, 2.