Biguanides for type 2 diabetes


Generic Name Brand Name
glipizide and metformin Metaglip
metformin Glucophage, Glucophage XR
metformin and glyburide Glucovance
repaglinide and metformin Prandimet
rosiglitazone and metformin Avandamet

Glyburide and glipizide are sulfonylurea medications, which lower blood sugar by causing the pancreas to release more insulin. Rosiglitazone is a thiazolidinedione medications, which lowers blood sugar by decreasing insulin resistance. Repaglinide is a meglitinide medication, which helps stop the rapid rise in blood sugar levels that can occur right after a person with type 2 diabetes eats. For more information, see the Medications section of the topic Type 2 Diabetes: Recently Diagnosed.

In some cases, a doctor may recommend metformin for people who have prediabetes.

How It Works

The action of biguanides in treating type 2 diabetes is not completely understood. They lower blood sugar by:

  • Decreasing the amount of sugar produced by the liver. This is the primary action of these medicines.
  • Increasing the amount of sugar absorbed by muscle cells and decreasing the body's insulin resistance.

Metformin does not cause the pancreas to produce more insulin. And when taken alone, it should not cause low blood sugar (hypoglycemia) or weight gain. Some people taking metformin may lose weight.

Metformin may lower the amount of fat (triglycerides) in the bloodstream, which may reduce the risk of heart disease. It also has been shown to reduce certain abnormal clotting factors and markers of inflammation that can lead to hardening of the arteries.

Why It Is Used

These medicines can be used to treat people with type 2 diabetes who have not been able to keep their blood sugar levels within your target range by eating a balanced diet, losing weight, and exercising regularly. Metformin may be used alone or along with a sulfonylurea or thiazolidinedione medication.

Metformin can also be used to treat people with type 2 diabetes who need to take insulin. A study showed that adding metformin to insulin therapy improved blood sugar levels better than increasing the dose of insulin and did not cause weight gain.1 Metformin may also be used with exenatide and sitagliptin.

People who have very low insulin levels, have other severe medical conditions (such as kidney, liver, heart, or lung disease), or are undergoing major surgery should not take biguanides.

Metformin is the oral medicine of choice for treating type 2 diabetes in children and adolescents.2

In some cases, a doctor may recommend metformin for people who have prediabetes.

How Well It Works

Results of the United Kingdom Prospective Diabetes Study showed that metformin:

  • Was as effective as sulfonylurea medications in reducing blood sugar levels in people with type 2 diabetes.3
  • Reduced the risk of complications from diabetes in people who were overweight. People who were overweight did not gain weight while taking metformin.4

People who have just been diagnosed with type 2 diabetes may be able to keep their blood sugar levels within a target range by taking metformin. But even though metformin controls blood sugar levels for a longer period of time than sulfonylurea medications, over time it may become less effective.

In studies, a combination of metformin and glyburide (Glucovance) caused a greater decrease in blood sugar levels than glyburide or metformin alone. Sometimes a combination of metformin and a sulfonylurea effectively controls blood sugar when a sulfonylurea medication alone has not been effective.

People usually do not gain weight and may even lose a small amount of weight when taking metformin. (People taking sulfonylurea medications or insulin may gain weight.)

Metformin is as effective in treating children with type 2 diabetes as it is in treating adults.2

Side Effects

The most common side effects of metformin are:

  • Temporary nausea.
  • Loss of appetite.
  • Diarrhea.
  • Increased abdominal gas.
  • A metallic taste.

These side effects occur in 5% to 20% of people taking metformin.3 Side effects usually decrease over time. When a person begins taking metformin, the dosage usually is increased gradually to prevent side effects. You may also reduce nausea by taking the medicine with food.

Blood levels of vitamin B12 can decrease in some people who take metformin, but this usually does not cause health problems.3

A rare side effect of metformin is a condition called lactic acidosis. Lactic acidosis develops when muscles release lactic acid during exercise. If the liver is not able to convert the lactic acid into sugar, the acid builds up in the blood. If lactic acidosis is not treated quickly, it can lead to coma and death.

  • Lactic acidosis may occur in people who have kidney or liver failure, have low levels of oxygen in their blood (hypoxia), abuse alcohol, or are dehydrated. It can also result if metformin is taken when a person has surgery or X-ray studies that use a dye. Be sure all your doctors know that you are taking this medicine if you need a test that involves the use of a dye or if you are having surgery. You will have to stop taking metformin at least 48 hours before the test or before surgery.
  • Metformin should not be used to treat diabetes in people who have decreased kidney or liver function. A blood test to measure kidney and liver function should be done before starting this medicine.

Metformin may decrease menstrual irregularities in women with polycystic ovary syndrome. This may increase the risk for unplanned pregnancy.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Biguanides do not cause low blood sugar (hypoglycemia) or weight gain, which are common side effects of the sulfonylurea medicines.

Metformin (Glucophage) has to be taken 2 to 3 times a day, but the extended-release form (Glucophage XR) can be taken only once a day. Both are available in generic form. Some people may have fewer gastrointestinal side effects with Glucophage XR than with Glucophage.

Although metformin may be safe to take during pregnancy, the U.S. Food and Drug Administration (FDA) has not approved it for that use. Talk with your doctor immediately if you become pregnant while taking metformin.

The effect of metformin may be increased if you also take cimetidine (Tagamet). Talk with your doctor if you are taking Tagamet.

The U.S. Food and Drug Administration (FDA) has announced a possible safety issue with the drug rosiglitazone (Avandia). A new study shows that people who take Avandia may raise their chance of having a heart attack. They may also raise their chance of death from heart disease.

Manufacturers of rosiglitazone (Avandia), pioglitazone (Actos), rosiglitazone and glimepiride (Avandaryl), rosiglitazone and metformin (Avandamet), and pioglitazone and glimepiride (Duetact) have added a warning that these drugs may cause heart failure or make heart failure worse in certain people.

If you take any of these medicines, do not stop taking them. Call your doctor to talk about which medicine is best for you.


Few studies have been done on the use of oral medicines for type 2 diabetes in children, and these medicines have not been approved by the U.S. Food and Drug Administration (FDA) for use in children. But because these oral medicines are safe for adults, most doctors use them to treat children with type 2 diabetes.

Metformin usually keeps blood sugar levels within a target range without increasing the likelihood that the child will gain weight. If after 3 to 6 months of treatment with metformin blood sugar levels are not consistently within your target range, a sulfonylurea or insulin is usually added.

Metformin should be stopped during an illness that causes vomiting or diarrhea or any condition that causes dehydration. Check with your doctor.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.



  1. Cheng AYY, Zinman B (2005). Principles of insulin therapy. In CR Kahn et al., eds., Joslin's Diabetes Mellitus, 14th ed., pp. 659–670. Philadelphia: Lippincott Williams and Wilkins.
  2. Jones KL, et al. (2002). Effect of metformin in pediatric patients with type 2 diabetes. Diabetes Care, 25(1): 89–94.
  3. Lebowitz HE (2005). Management of hyperglycemia with oral antihyperglycemic agents in type 2 diabetes. In CR Kahn et al., eds., Joslin's Diabetes Mellitus, 14th ed., pp. 687–710. Philadelphia: Lippincott Williams and Wilkins.
  4. Riddle MC, Genuth S (2007). Type 2 diabetes mellitus. In DC Dale, DD Federman, eds., ACP Medicine, section 9, chap. 2. New York: WebMD.

Last Updated: June 16, 2008

related physicians

related services

Bon Secours International| Sisters of Bon Secours USA| Bon Secours Health System

This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. Privacy Policy. How this information was developed to help you make better health decisions.

© 1995-2010 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.