Metformin Side Effects

Metformin is an oral diabetes medicine that helps control blood sugar levels.

Metformin is for people with type 2 diabetes. Metformin is sometimes used in combination with insulin or other medications, but it is not for treating type 1 diabetes.

Some people develop a life-threatening condition called lactic acidosis while taking metformin. You may be more likely to develop lactic acidosis if you have liver or kidney disease, congestive heart failure, a severe infection, if you are dehydrated, or if you drink large amounts of alcohol. Talk with your doctor about your individual risk.

You should not use this medication if you are allergic to metformin, or if you are in a state of diabetic ketoacidosis (call your doctor for treatment with insulin).

If you need to have any type of x-ray or CT scan using a dye that is injected into your veins, you will need to temporarily stop taking metformin.

To make sure you can safely take metformin, tell your doctor if you have any of these other conditions:

  • liver disease; or
  • a history of heart disease.

FDA pregnancy category B. Metformin is not expected to be harmful to an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant during treatment. It is not known whether metformin passes into breast milk or if it could harm a nursing baby. Do not take metformin without first talking to your doctor if you are breast-feeding a baby. Metformin should not be given to a child younger than 10 years old. Extended-release metformin (Glucophage XR) should not be given to a child younger than 17 years old.

Get emergency medical help if you have any of these signs of an allergic reaction to metformin: hives; difficult breathing; swelling of your face, lips, tongue, or throat. This medication may cause lactic acidosis (a build-up of lactic acid in the body, which can be fatal). Lactic acidosis can start slowly and get worse over time. Get emergency medical help if you have even mild symptoms of lactic acidosis, such as:

  • muscle pain or weakness;
  • numb or cold feeling in your arms and legs;
  • trouble breathing;
  • feeling dizzy, light-headed, tired, or very weak;
  • stomach pain, nausea with vomiting; or
  • slow or uneven heart rate.

Call your doctor at once if you have any other serious side effect such as:

  • feeling short of breath, even with mild exertion;
  • swelling or rapid weight gain; or
  • fever, chills, body aches, flu symptoms.

Less serious metformin side effects may include:

  • headache or muscle pain;
  • weakness; or
  • mild nausea, vomiting, diarrhea, gas, stomach pain.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

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