Emergency contraception effectiveness
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Emergency Contraception Methods and Effectiveness
Several emergency contraception (EC) methods are available, including hormonal pills (levonorgestrel, mifepristone, ulipristal acetate, and the Yuzpe regimen) and the copper intrauterine device (Cu-IUD). The effectiveness of these methods varies, with some being more effective and having fewer side effects than others 1259.
Levonorgestrel and Mifepristone: High Efficacy and Fewer Side Effects
Levonorgestrel and mifepristone are among the most effective EC pills. Levonorgestrel can prevent about 85% of expected pregnancies and is more effective and better tolerated than the older Yuzpe regimen, which prevents about 74% of pregnancies but causes more side effects, especially nausea and vomiting 1245+1 MORE. Mifepristone, especially at mid-dose (25–50 mg), is even more effective than levonorgestrel and the Yuzpe regimen, but it can cause a delay in the next menstrual period, which is dose-related 259. Both low- and mid-dose mifepristone are probably more effective than levonorgestrel, but low-dose mifepristone is less effective than mid-dose 59.
Ulipristal Acetate and Copper IUD: Additional Options
Ulipristal acetate (UPA) is another EC option and may be more effective than levonorgestrel, especially when taken closer to ovulation 56. The copper IUD is the most effective EC method, preventing over 90% of pregnancies, and can also provide ongoing contraception, but it may cause more abdominal pain compared to pills 159.
Timing and Effectiveness
All EC methods are more effective the sooner they are used after unprotected intercourse. The effectiveness of both the Yuzpe regimen and levonorgestrel decreases as the time between intercourse and treatment increases 13. However, EC pills can still significantly reduce the risk of pregnancy even when taken between 72 and 120 hours after intercourse, though their effectiveness is lower than when taken within 72 hours .
Effectiveness in Special Populations
For women weighing 80 kg or more, recent research found no significant differences in pregnancy rates between different EC regimens (levonorgestrel 1.5 mg, levonorgestrel 3.0 mg, and ulipristal acetate 30 mg), but the study was limited by a small sample size and could not definitively determine if weight affects EC effectiveness .
Emergency Contraception After Sexual Assault
Single-dose levonorgestrel EC is highly effective in preventing pregnancy after sexual assault, with a failure rate of less than 1% in a clinical setting .
Side Effects and Considerations
Nausea and vomiting are the main side effects of EC, especially with the Yuzpe regimen. Levonorgestrel and mifepristone have fewer side effects, with mifepristone mainly causing menstrual delay 1259. Ulipristal acetate may delay menstruation more than levonorgestrel .
Conclusion
Levonorgestrel and mifepristone are the most effective and well-tolerated emergency contraceptive pills, with mifepristone being slightly more effective but more likely to delay menstruation. The copper IUD is the most effective overall but may not be suitable for everyone. All EC methods work best when used as soon as possible after unprotected intercourse, and they remain effective up to 120 hours, though efficacy decreases with time. Emergency contraception is a reliable option for preventing pregnancy after unprotected sex, but ongoing regular contraception is more effective for long-term prevention 1234+6 MORE.
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