**Study Summary:** This study is about using a device called Mirena to treat a condition in women called nonatypical endometrial hyperplasia (NAEH). NAEH happens when the lining of the uterus (the endometrium) becomes too thick but is not cancerous. This can cause unusual bleeding. If not treated, it might lead to cancer. Mirena, a type of birth control, releases a hormone called progesterone to help balance hormones and treat NAEH. **Key Points**: - **Treatment Duration**: Participants will use Mirena or take a pill daily for 6 months. - **Study Length & Visits**: The study lasts about 10 months with 5 clinic visits. - **Procedures & Tests**: Include blood/urine tests, ultrasounds, and a hysteroscopy (using a camera to see inside the womb). Participants must be women aged 18 or older with confirmed NAEH. They cannot have certain medical conditions or be pregnant. Researchers will track any health issues that arise during the study.

Note: Consider joining if you meet the criteria and are comfortable with the procedures.