Biguanides work by:

  • decreasing the liver's production of glucose
  • decreasing the small intestines' absorption of glucose
  • improving your body's ability to use insulin, by improving your insulin sensitivity

These actions work together to lower the amount of glucose in your blood.


You may lose a few pounds when you start to take a biguanide. This weight loss can help you control your blood glucose levels even more. Biguanides can also improve your blood fat and cholesterol levels.


Possible Side Effects of Biguanides

Talk with your doctor if you think this medication is causing side effects.


Bothersome Side Effects

You may have these side effects when you take a biguanide:

  • diarrhea
  • stomach upset, including nausea
  • diminished appetite
  • metallic taste in mouth


Serious Side Effects

Biguanides can cause a rare but very serious condition called lactic acidosis. This is primarily a concern in people with kidney problems or heart failure. Symptoms of lactic acidosis include:

  • weakness
  • tiredness
  • unusual muscle pain
  • dizziness
  • feeling cold
  • sudden slow, irregular heartbeat
  • trouble breathing

You should call your doctor immediately if you have any of these symptoms because they can lead to death.


Not everyone who takes biguanides will have these side effects. You should not be afraid to take your medicine because of the side effects listed. They are listed so that you can watch out for them and tell your doctor right away if you experience any of them.


Possible Drug Interactions With Biguanides

Before you take a biguanide, tell all your doctors and your pharmacist about all the medicines you take. Include medicines you take for your diabetes as well as for any other problem. Tell them about everything you take and how much you take each day, including all of the following:

  • prescription medicines
  • over-the-counter medicines
  • herbs
  • vitamin and mineral supplements

It's best to keep an updated list of these and bring a copy to give to your doctor. That way you can add to it whenever you take something new or delete the types you no longer take. Make a copy for each of your doctors so that they can keep it in your file. This complete list helps your doctor be better prepared to prescribe diabetes pills that are the least likely to interact with your other treatments.


Talk to your doctor about whether you can drink alcohol when you take biguanides. Drinking alcohol can lead to hypoglycemia (low blood glucose), which can be dangerous.

Biguanides are used in combination with many other types of diabetes pills. Using pills that act in different ways in combination may be more effective than using either one on its own. But because they have similar actions, you should monitor your blood glucose levels closely. Ask your doctor what to do if you take biguanides with other diabetes pills.

Many medicines can have harmful effects when you take them with other medicines. Always tell your doctor about all the medicines that you take. Do not use any other medicine without your doctor's OK. Talk with your doctor before you take a biguanide if you take any other medicines.

Written by award-winning health writer Bobbie Hasselbring

Reviewed by Beth Seltzer, MD

Last updated June 2008