Biguanides for Diabetes: Metformin

Reviewed by Michael Dansinger, MD on May 09, 2019

Metformin is a biguanide, part of a family of compounds that share a similar chemical form. They're used to make drugs and disinfectants.

This drug helps people with type 2 diabetes and prediabetes bring down their blood sugar level in three ways:

  • It tells your liver to make less glucose.
  • It lowers your insulin resistance, which means it makes your muscles use insulin better so glucose can get into them instead of staying in your blood.
  • It helps your intestines absorb less glucose from your food.

It can lower your A1c, the "average" of your blood sugar control over a few months. It can also delay prediabetes becoming diabetes.

Metformin Medications

It's usually the first medicine doctors prescribe for type 2 diabetes. Some brand names are:

All of those are pills except Riomet, which is a liquid.

Some "combination" pills have metformin with another medicine, including:

Side Effects

If you're taking a combination pill, or metformin with other diabetes medications or insulin, check with your doctor about how likely you are to have low blood sugars. If you're taking metformin by itself, you probably won't have low blood sugars.

You might see the shell part of an extended-release pill in your poop. If you do, don't worry. The medication has gone into your body, and you shouldn't take any extra pills.

Metformin can cause problems in your gut, but they usually go away in a few weeks. You could have:

They could come back if your doctor raises your dose. Taking metformin with food can help.

While doctors used to avoid prescribing this drug to people who've had kidney trouble, it may be OK for someone with mild or moderate kidney disease.

When you use metformin for a long time, it could lower the amount of vitamin B-12 in your body too much. Your doctor may want to check your B-12 level, especially if you have anemia or nerve damage in your feet or hands (peripheral neuropathy).

One large study has linked long-term metformin use to higher chances of getting Alzheimer's disease and Parkinson's disease. But we need more research to understand the connection better and what it means.

Lactic Acidosis

Some people who take metformin can get a lactic acid buildup in their blood. It's rare and more likely to happen if you:

It's serious, so call your doctor right away when you:

Before Surgery, X-rays, or Scans

If you're going to have surgery, or any kind of X-ray or scan that uses dye injected into your body, let your health team know that you take metformin. You may have to stop taking it for a few days so the procedure goes well, but you'll need to talk to your doctor first about how to control your blood sugar.

WebMD Medical Reference



American Diabetes Association: "What Are My Options?"

Diabetes Care: "Standards of Medical Care in Diabetes -- 2017," "Quantifying the Effect of Metformin Treatment and Dose on Glycemic Control."

FDA: "Metformin Information," "FDA Revises Warnings Regarding Use of the Diabetes Medicine Metformin in Certain Patients with Reduced Kidney Function."

Joslin Diabetes Center: "Oral Diabetes Medications Summary Chart."

University of Wisconsin Health: "Metformin."

Medscape: "Metformin Use Linked to Increased Dementia, Parkinson's Risk in Patients With Diabetes."

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