Emergency contraception.

Knowledge and use of emergency contraception world-wide is extremely limited. Recent research has demonstrated that levonorgestrel alone is at least as effective as the Yuzpe regimen and is much better tolerated. Levonorgestrel is likely to become the method of choice in the early 21st century. Mifepristone is highly effective even at doses which are not abortifacient. Efficacy cannot be calculated precisely, but all presently available methods seem to prevent at least 74% of unwanted pregnancies. The Yuzpe regimen inhibits or delays ovulation, but there is no good evidence that it prevents implantation. There are no data on the mechanism of action of levonorgestrel alone and the mode of action of mifepristone depends on when in the reproductive cycle it is used. Accessibility to emergency contraception is limited by the requirement for it to be prescribed by a doctor. Advanced provision of emergency contraception may prevent a significant number of unwanted pregnancies.