What is the most effective form of emergency contraception?

The copper intrauterine device (IUD) is recognized as the most effective form of emergency contraception. It has a failure rate of less than 1% when inserted within five days following unprotected intercourse. This high level of efficacy is largely attributed to the copper's ability to create an environment that is toxic to sperm, inhibiting fertilization. Additionally, if fertilization has already occurred, the copper IUD may prevent implantation of a fertilized egg.

While levonorgestrel pills and ulipristal acetate are both effective forms of emergency contraception, their failure rates are higher compared to the copper IUD. Levonorgestrel is most effective when taken within 72 hours but can be used up to 5 days with diminishing efficacy, while ulipristal acetate remains effective for up to 120 hours, with a higher efficacy than levonorgestrel but still not matching that of the copper IUD. The contraceptive patch, on the other hand, is not a form of emergency contraception and is designed for regular contraceptive use.

In summary, the copper IUD stands out for its exceptional efficacy and dual purpose as a long-term contraceptive method, making it the top choice for emergency contraception.