The copper changes the pH in your uterus and makes it a hostile environment. It's a two-tiered birth control like the pill in that it works against both fertilization and implantation. It helps prevent conception by creating a hostile environment for the sperm, and if conception does occur it helps prevent implantation by making a hostile environment for the fertilized egg.
I had the paraguard twice, and my only side effect was heavier periods. To me it was preferable to a hormonal birth control because I tend to have very severe side effects from those, and much preferable to the mess and inconvenience of barrier methods.
Talk to your doc about the side effects and your specific risks for the side effects based on your health history to see if you are a good match.
at 9:57 AM on Oct. 28, 2009