Of the three women I personally know who had a Mirena, all 3 became hypothyroid, probably the result of an autoimmune attack on the thyroid gland. Lots of women develop autoimmune diseases and/or symptoms, probably from the silicone in the IUD. Your confused immune system senses the presence of the foreign body, gets confused and your body attacks itself. You can do a search under this forum and read all the stories. It's quite common with the Mirena.