An IUD is a small, T-shaped piece of plastic that is inserted into the uterus by your doctor. The effectiveness is about 99%. Once the IUD is inserted, it offers protection for 5 to 10 years depending on the IUD used. A Mirena IUD is a hormone containing IUD which has the added benefit of less menstrual flow and cramping. Paragard is a hormone free IUD. The most common side effects of Paragard are heavier menstrual cycles and cramping.