Safe drug lowers diabetes risk in women with PCOS

Safe drug lowers diabetes risk in women with PCOS

The Medicine Cabinet: Ask the Harvard Experts 

By Howard LeWine, M.D.

Q: My daughter has polycystic ovary syndrome. Her new doctor prescribed metformin. But she doesn’t have diabetes. How is metformin helpful?

A: A little background on polycystic ovary syndrome (PCOS) first.

Normally the ovaries produce estrogen, progesterone and only a small amount of testosterone. But between 4 percent and 7 percent of women produce too much testosterone. These women have a pattern of symptoms called polycystic ovary syndrome.

With too much testosterone, the eggs are not always released from their follicles in the ovaries. The ovaries appear to contain cysts because the fluid-filled follicles don’t always open and empty.

Women with polycystic ovary syndrome may have problems with fertility because egg release (ovulation) does not always occur. With the abnormal hormone balance, menstrual periods are often irregular. Polycystic ovary syndrome can also cause cosmetic effects such as acne and facial hair growth.

Many women with polycystic ovary syndrome have high levels of insulin and resistance to insulin’s effects. This puts them at risk for developing diabetes. This is why doctors will prescribe metformin in women with PCOS. The drug reduces insulin resistance and helps prevent diabetes.

Metformin keeps blood sugar levels from rising by decreasing the amount of sugar produced by the liver and improving the action of insulin to help move sugar out of the blood stream and into cells.

But it almost never leads to an abnormally low sugar in people with or without diabetes. (This is true if metformin is not being used at the same time as other treatments for diabetes.)

Common side effects of metformin use include loose stools or diarrhea, a metallic taste in the mouth and nausea.

Metformin is safe for most people. However, people with advanced kidney or liver disease should avoid it.

Metformin is less likely to help with some of the other problems related to PCOS, such as irregular menstrual periods, acne, facial hair and infertility. There are better therapies available to address these issues.

(Howard LeWine, M.D. is an internist at Brigham and Women’s Hospital in Boston and assistant professor of medicine at Harvard Medical School. For additional consumer health information, please visit