How effective are IUDs?
The theoretical effectiveness rate of IUDs are 99.9% (Mirena® (Levonorgestrel)) and 99.4% (ParaGard® (copper)). These rates are based on studies that have been done to determine how effective a method itself can be, apart from user behaviors. Actual effectiveness rates are 99.9% and 99.2% respectively, which reflectss what happens to the pregnancy rate in a group of people who do not use this method correctly some of the time and who do not use this method every time they have intercourse.
