Quote Originally Posted by Irulan
it irritates the uterine lining to prevent implantation. You can leave them in for years with the caveats that Doc stated: single partner, no STD's etc. There are some versions that release progesterone. It is inserted when you are mensrtuating.

http://www.fwhc.org/birth-control/iudinfo.htm has some good general information.

Irulan
Hrm. Just reading that page gives me the willies. I know that hormones aren't a simple matter, but somehow they scare me less than having something floating around inside me. Guess it's a good thing there are several different methods available.