PCOS occurs when a woman does not release an egg regularly each month, causing her periods to be irregular. Women with PCOS can also have increased hair growth on the face and body, acne, head balding, infertility, pre-diabetes, and diabetes. PCOS is commonly treated with oral contraceptive pills (also known as the birth control pills). Sometimes, a medication called metformin is also used to treat PCOS, especially if a woman has evidence of insulin resistance or if fertility is desired. Unfortunately, metformin works in only some women with PCOS. The mechanism through which metformin works in PCOS is not clear and it difficult to predict who will benefit from metformin treatment and who will not.

The investigators are doing this research study to look at how the medication metformin affects the cells in the body of patients with PCOS. Specifically, the investigators will look at how metformin affects the mitochondria. Mitochondria are the part of cells that produce fuel (energy) for other cells and play a role in metabolism. The investigators would like to see whether there is a relationship between mitochondrial activity and symptoms of polycystic ovary syndrome (PCOS) before and after treatment with metformin. They would also like to study whether genes affect the response to metformin in women with PCOS.

Women who are eligible to enroll in this study will be treated with the medication metformin for 12 weeks. Before and after treatment with metformin, the following will be assessed:

• Weight, blood pressure, waist circumference
• Lipids (cholesterol)
• Hormone levels (including testosterone and other androgens)
• IV glucose tolerance test (to assess for early evidence of insulin resistance)
• Effect of metformin on muscle mitochondria (this will involve one MRI scan and one muscle biopsy each before and after treatment with metformin)

Ovulation will be closely monitored at least twice a month with pelvic ultrasounds and blood tests for estrogen and progesterone levels.

Inclusion Criteria:

• Polycystic ovary syndrome
• No hormonal or antidiabetic medications for 1 month
• Good general health

Exclusion Criteria:

• Smoker
• Acute infection or chronic disease
• Diabetes
• Pregnant or trying to get pregnant over next half year
• Bleeding disorders
• Any metal or foreign implants (e.g., aneurysm clips, ear implants, heart pacemakers or defibrillators)