One of the biguanide drugs, which cut the liver's glucose production.

One of the biguanide drugs, which cut the liver's glucose production.(IMMUNODEFENCE.COM)

Even if you don't take metformin, you've probably heard of this popular diabetes drug. Nearly 35 million prescriptions of the generic form of the drug were sold in the U.S. in 2006, making it one of the top-10 best-selling generic drugs.

Metformin is also sold under the brand names Glucophage and Glucophage XR, and is found in pills that combine two types of antidiabetes medication, such as Glucovance and Metaglip (which combine metformin with a sulfonylurea drug) and Avandamet (a combination of metformin and rosiglitazone, a thiazolidinedione medication).

Metformin is a biguanide, a drug that reduces the amount of glucose that the liver makes and improves the body's use of insulin. The U.S. Food and Drug Administration approved it in 1995, but it has been used in Europe, Canada, and other countries for much longer.

Metformin has a long safety record

In 2006 the American Diabetes Association recommended it as the first drug of choice for patients, edging out sulfonylureas, a class of drug used since the 1950s that is more likely to cause weight gain and hypoglycemia.

Metformin's decade-long safety record may come as a relief for people who remember another drug in that class, phenformin. That drug was pulled from the U.S. market in the 1970s due to an increased risk of lactic acidosis, a potentially fatal buildup of lactic acid in the blood.

After the phenformin scare, many people were skittish about using a drug in the same class of medications, says Richard Hellman, MD, former president of the American Association of Clinical Endocrinologists. But after more than a decade of metformin's use in the U.S., those worries have been allayed. "It's a common mainstay; it's a very good drug," Dr. Hellman says.

Studies show it beats out other drugs

A recent study in the Annals of Internal Medicine showed that metformin gets the job done. Using data from 216 previous controlled trials studies and two reviews, researchers at Johns Hopkins University in Baltimore compared the benefits and risks of various oral diabetes medications.

Overall, metformin came out on top, proving just as good, or better, than other medications at controlling blood sugar and cholesterol.

Gastrointestinal side effects

The only real downside in the study was that metformin was linked with a higher rate of gastrointestinal problems, including gas, nausea, vomiting, and abdominal pain. Many people, though, do just fine or adjust to the drug with time.

"I have no problems with metformin," reports Lisa Moore, 25, a family education coordinator in Austin, Texas. She also has a friend with prediabetes who takes it as a preventive (metformin can reduce your chances of getting diabetes if you're at high risk); she is actually taking more metformin than Moore without any problems.

For Dick Robbins, 72, of Hot Springs Village, Ark., it took some time to get used to metformin. "I would go from diarrhea, to constipation and diarrhea, to constipation. Now my body has adjusted to the dosage and I'm having no problem with it."