[Bias in publications about the mechanism of action of the morning-after pill].

The morning-after pill or ECP (levonorgestrel) first came into use in the late 20th century, but has only become widely available in the last ten years. Its introduction has been facilitated by health policies which have led to the removal of certain obstacles hindering its use. In this context, sociological, statistical and scientific data have been employed which have often turned out to be biased or partial in nature. The reliability of the information provided by health authorities, pharmaceutical companies and other social entities has been called into question in various respects, particularly as far as the mechanism of action, side effects and pregnancy rate are concerned. This study focuses on the mechanism by which levonorgestrel acts, since a wider discussion would fall beyond the scope of a single study, and the mechanism of action is the aspect which is least understood and most controversial. It remains to be determined whether levonorgestrel is a product which only acts prior to ovulation or which has an effect on the human embryo.