Oral Diabetes Medications


Metformin (Glucophage), which is also available in an extended release form (Glucophage XR, Glumetza), is the only biguanide sold in the United States. It acts primarily by decreasing the liver's production of glucose. It also increases the amount of glucose that is transported into cells.

Metformin is often the first drug that doctors prescribe for type 2 diabetes because of the following advantages:

  • Its effects do not involve beta cells, so it works even in people with little beta-cell function.
  • It doesn't cause hypoglycemia when used alone.
  • It doesn't cause weight gain and may even produce weight loss. (In one study, people taking metformin lost almost 6 lbs, on average.)

On the negative side, about 30 percent of people taking metformin develop gastrointestinal side effects such as diarrhea, nausea, bloating, and gas, which often disappear over time. Metformin should not be taken by people with alcoholism, kidney or liver disease, heart failure, or severe emphysema or other chronic lung diseases, because it increases the risk of life-threatening lactic acidosis (buildup of lactic acid in the blood).

Metformin is often prescribed for obese people who are insulin resistant—that is, people who develop high blood glucose levels because their body's cells have become less sensitive to the action of insulin. It can be used either as a first-line treatment (the first drug tried) or as a second-line choice for people who do not achieve adequate glucose control with a sulfonylurea. Studies have shown that metformin, taken alone, can reduce blood glucose levels by about 20 percent and can boost the glucose-lowering effects of a sulfonylurea by an additional 25 percent.

Metformin is also prescribed in combination with a meglitinide, an alpha-glucosidase inhibitor, a thiazolidinedione, or insulin. Several of these combinations are sold as a single pill: Actoplus Met (metformin and pioglitazone), Avandamet (metformin and rosiglitazone), Glucovance (metformin and glyburide), and Metaglip (metformin and glipizide).

Publication Review By: Written by: Christopher D. Saudek, M.D.; Simeon Margolis, M.D., Ph.D.

Published: 21 Apr 2009

Last Modified: 10 Mar 2015