abnormal uterine bleeding
"To anyone thinking about the getting the Mirena.... expect to bleed for weeks afterwards but don't be worried. I've had mine for 3 years now and haven't had a period in 2 years. I've spotted once or twice but my periods weren't bad in the first place. Everyone's different. The insertion was PAINFUL and at first I bleed for 4-6 weeks with bad cramps. It was horrible but I'm glad I stuck it out. The piece of mind I get from such an effective birth control was worth the rough beginning."