Hi, Mirena IUD (intrauterine device) contains levonorgestrel which is used to prevent pregnancies from unprotected sexual intercourses and to treat heavy menstrual periods. Mirena IUD only contains a progestin called levonorgestrel which is similar to woman s natural hormone, progesterone. It is a small T shaped device plastic device that acts as long term birth control method. As Mirena IUD (intrauterine device) only releases progesterone, so progesterone levels increase in your body. On the other hand, it doesn t release estrogen, so estrogen levels naturally decrease in your body. Changes in estrogen as well as progesterone levels can affect your hypothalamus of the brain that regulates internal temperature and can lead to develop premenstrual syndrome (PMS) like symptoms such as hot flashes, night sweats, flushed skin, sleeping difficulties etc. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician