This study will test whether metformin administration can ameliorate androgen (male hormone) overproduction in overweight pubertal girls with androgen excess. The investigators hypothesize that improvement in insulin sensitivity by 12 weeks of metformin administration will improve androgen levels after adrenal stimulation testing with adrenocorticotropic hormone (ACTH) or ovarian stimulation testing with recombinant human chorionic gonadotropin (rhCG).

Inclusion Criteria:

• Overweight(>85th BMI%) females
• Early to late puberty (expected age range 7-18)
• Hyperandrogenemic (free testosterone greater than 2.5 standard deviations above the mean for normal control subjects of the same Tanner Stage)
• Screening labs within age-appropriate normal range, with the exception of a mildly low hematocrit (see below) and the hormonal abnormalities inherent in obesity which could include mildly elevated luteinizing hormone (LH), lipids, testosterone, prolactin, DHEAS, E2, glucose, and insulin; and decreased follicle-stimulating hormone (FSH) and/or sex hormone-binding globulin (SHBG)

Exclusion Criteria:

• Age < 7 or > 18 y
• Inability to comprehend what will be done during the study or why it will be done
• BMI-for-age < 5th percentile
• Positive pregnancy test or lactation.
• Abnormal laboratory studies will be confirmed by repeat testing to exclude laboratory error.
• Morning cortisol < 3 µg/dL or history of Cushing syndrome or adrenal insufficiency
• History of congenital adrenal hyperplasia or 17-hydroxyprogesterone > 300 ng/dL, which suggests the possibility of congenital adrenal hyperplasia (if postmenarcheal, the 17-hydroxyprogesterone will be collected during the follicular phase, or ≥ 40 days since last menses if oligomenorrheic). NOTE: If a 17-hydroxyprogesterone >300 mg/dL is confirmed on repeat testing, an ACTH-stimulated 17-hydroxyprogesterone <1000 ng/dL will be required for study participation.
• Total testosterone > 150 ng/dL, which suggests the possibility of a virilizing neoplasm
• DHEAS greater than the upper limit of age-appropriate normal range (mild elevations may be seen in polycystic ovary syndrome (PCOS) and adolescent hyperandrogenemia (HA), and elevations < 1.5 times the age-appropriate upper limit of normal will be accepted in these groups)
• Virilization
• Previous diagnosis of diabetes, fasting glucose ≥126 mg/dL, or a hemoglobin A1c ≥6.5%
• Abnormal thyroid stimulating hormone (TSH) for age. Subjects with stable and adequately treated hypothyroidism, reflected by normal TSH values, will not be excluded.
• Abnormal prolactin. Mild elevations may be seen in overweight girls, and elevations <1.5 times the upper limit of normal will be accepted in this group.
• Persistent hematocrit <36% and hemoglobin <12 g/dL. Subjects with a mildly low hematocrit (33-36%) will be asked to take iron in the form of ferrous gluconate for up to 60 days. Subjects weighing ≤ 36 kg will take one 300-325 mg tablet oral ferrous gluconate daily (containing 36 mg elemental iron);subjects weighing >36 kg will take two 300-325 mg tablets oral ferrous gluconate daily (containing 36 mg elemental iron each). They will return to the Clinical Research Unit (CRU) after 30-60 days of iron therapy to have their hemoglobin or hematocrit rechecked and will proceed with the remainder of the study if it is ≥12 g/dL or ≥36%, respectively.
• Persistent liver test abnormalities, with the exception that mild bilirubin elevations will be accepted in the setting of known Gilbert's syndrome. Mild elevations may be seen in overweight girls, so elevations <1.5 times the upper limit of normal will be accepted in this group.
• Significant history of cardiac or pulmonary dysfunction (e.g., known or suspected congestive heart failure; asthma requiring intermittent systemic corticosteroids; etc.)
• Abnormal sodium, potassium, or bicarbonate concentrations, or elevated creatinine concentration (confirmed on repeat)
• No medications known to affect the reproductive system or glucose metabolism can be taken in the 3 months prior to the study. Such medications include oral contraceptive pills, progestins, metformin, glucocorticoids, and psychotropics.