This study will assess the affects of an estradiol hemihydrate transdermal system on bone health in 24 adolescent females aged 12-19 years old with anorexia nervosa. Participants in this study will be randomized 1:1 into 2 groups. One group will receive treatment with a transdermal estrogen patch and the other group will not.

Currently, no therapy exists to improve bone health in females with anorexia nervosa (AN) other than improving body mass. Transdermal estrogen is being investigated as to whether it has benefit to bone health parameters. While numerous studies have sought to orally replace estrogen in adolescents and women with AN, the replacement therapy suppresses IGF-1, and as a result oral estrogen studies have demonstrated no bone health benefit in AN. However, transdermal physiologic estrogen, due to no first-pass metabolism in the liver, is not IGF-1 suppressive. IGF-1 is known to be hormone that directly affects bone formation and is considered to be osteoanabolic (helps increase bone mass).