The purpose of this study is to see if metformin will be effective in making endometrial hyperplasia without atypia better by returning the tissue to a normal state.

This is a multi-institutional pilot clinical trial designed to estimate the response rate and safety of metformin for the treatment of simple and complex endometrial hyperplasia (EH) without atypia. Enrollment of patients will occur at UNC-Chapel Hill and Southern Pines Women's Health Center. Fifteen patients will be enrolled over the course of 1 year. Metformin will be initiated at 850 mg orally once daily, and titrated up to twice daily over a minimum of 1 months time. Treatment will last 12 weeks and then patients will undergo repeat endometrial biopsy to assess for regression or persistence of EH.

Inclusion Criteria:

• Be between the ages of 18-75 years old
• Have a confirmed diagnosis of endometrial hyperplasia without atypia based upon endometrial biopsy
• Have no contraindications to short-term metformin therapy
• Have a creatinine clearance of ≥ 90 ml/min, as calculated by the Cockroft-Gault formula
• Have normal serum transaminase values (AST and ALT)
• Need to be able to undergo metformin treatment for a duration of 12 weeks prior to repeat endometrial biopsy

Exclusion Criteria:

• Are currently taking metformin or have taken metformin in the past 6 months or have a history of an allergic reaction or intolerance at any time to metformin
• Have a history of liver or renal dysfunction.
• Have a random glucose of ≤ 65 or ≥ 200
• Have a recent history of alcoholism. Former alcoholics who have abstained from alcohol for 5 years or more may be enrolled in this study.
• Have a history of vitamin B12 deficiency
• Are pregnant
• Are currently taking insulin
• Are taking a drug that may significantly interact or influence the metabolism of metformin
• In the opinion of the investigator, the patient is felt not to be appropriate for the study