Emergency contraception (EC) effectiveness varies by type and timing. Here’s a breakdown of how effective each option typically is:
1. Levonorgestrel-based Pills (e.g., Plan B One-Step)
• Effectiveness: Around 87% when taken within 72 hours after unprotected sex. It reduces the risk of pregnancy by about 50-89% when used correctly.
• Timing Impact: The sooner it’s taken, the better. It’s most effective within 24 hours and begins to lose efficacy after 72 hours, though it can still work up to 5 days (120 hours).
• BMI Consideration: Its effectiveness decreases with higher body weight (BMI over 25), though it may still offer some protection.
2. Ulipristal Acetate (e.g., Ella)
• Effectiveness: Around 85-95%, and considered more effective than levonorgestrel, particularly between 72 and 120 hours after unprotected sex.
• Timing Impact: Remains effective for the full 5 days after unprotected sex, with consistent effectiveness throughout this window.
• BMI Consideration: Somewhat less affected by higher body weight than levonorgestrel, though effectiveness may still be lower for people with a BMI over 30.
3. Copper IUD (e.g., Paragard)
• Effectiveness: Over 99% effective as emergency contraception, regardless of when it’s inserted within the 5-day window.
• Timing Impact: Effective for the full 5-day window after unprotected sex and is not dependent on timing within this period.
• BMI Consideration: Its effectiveness is not affected by body weight.
4. Combined Oral Contraceptive Pills (Yuzpe Method)
• Effectiveness: About 75%, less effective than the above methods and more likely to cause side effects like nausea.
• Timing Impact: Best used as soon as possible, but it’s generally less effective than dedicated EC pills or the copper IUD.
Factors Affecting Effectiveness
• Timing: All EC options work best when used as soon as possible after unprotected sex.
• BMI: Higher body weight can reduce the effectiveness of levonorgestrel and, to a lesser extent, ulipristal acetate. A copper IUD is recommended in these cases for optimal effectiveness.
• Ovulation Timing: EC works by delaying ovulation. If ovulation has already occurred, these methods may not be effective.
In summary, the copper IUD is the most effective form of emergency contraception. Pills like levonorgestrel and ulipristal acetate are highly effective, particularly when used promptly. None of these methods provide guaranteed prevention, but all can significantly reduce the chance of pregnancy.
