What is metformin?

Metformin is an oral diabetes medicine that helps control blood sugar levels. Metformin is used together with diet and exercise to improve blood sugar control in adults with type 2 diabetes mellitus.

Metformin is sometimes used together with insulin or other medications, but it is not for treating type 1 diabetes.

Important information

You should not use metformin if you have severe kidney disease or diabetic ketoacidosis (call your doctor for treatment).

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.

This medicine may cause a serious condition called lactic acidosis. Get emergency medical help if you have even mild symptoms such as: muscle pain or weakness, numb or cold feeling in your arms and legs, trouble breathing, stomach pain, nausea with vomiting, slow or uneven heart rate, dizziness, or feeling very weak or tired.

Metformin side effects

Get emergency medical help if you have signs of an allergic reaction to metformin: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Some people develop lactic acidosis while taking this medicine. Early symptoms may get worse over time and this condition can be fatal. Get emergency medical help if you have even mild symptoms 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.

Common metformin side effects may include:

• low blood sugar;
• nausea, upset stomach; or
• diarrhea

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Before taking this medicine

You should not use metformin if you are allergic to it, or if you have:

• severe kidney disease; or
• metabolic or diabetic ketoacidosis (call your doctor for treatment).

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 this medicine is safe for you, tell your doctor if you have ever had:

• kidney disease (your kidney function may need to be checked before you take this medicine);
• high ketone levels in your blood or urine;
• heart disease, congestive heart failure;
• liver disease; or
• if you also use insulin, or other oral diabetes medications.

Some people taking metformin develop a serious condition called lactic acidosis. This may be more likely if you have liver or kidney disease, congestive heart failure, surgery, a heart attack or stroke, a severe infection, if you are 65 or older, if you are dehydrated, or if you drink a lot of alcohol. Talk with your doctor about your risk.

Follow your doctor’s instructions about using this medicine if you are pregnant. Blood sugar control is very important during pregnancy, and your dose needs may be different during each trimester of pregnancy. Tell your doctor if you become pregnant while taking metformin.

It is not known whether metformin passes into breast milk or if it could harm a nursing baby. You should not breast-feed while using this medicine.

Metformin should not be given to a child younger than 10 years old. Some forms of metformin are not approved for use by anyone younger than 18 years old.

How should I take metformin?

Take metformin exactly as prescribed by your doctor. Follow all directions on your prescription label. Your doctor may occasionally change your dose. Do not use this medicine in larger or smaller amounts or for longer than recommended.

Take metformin with a meal, unless your doctor tells you otherwise. Some brands of this medicine are taken only once daily with the evening meal. Follow your doctor’s instructions.

Do not crush, chew, or break an extended-release tablet. Swallow the tablet whole.

Measure liquid medicine with the dosing syringe provided, or with a special dose-measuring spoon or medicine cup. If you do not have a dose-measuring device, ask your pharmacist for one.

Some tablet forms of metformin are made with a shell that is not absorbed or melted in the body. Part of the tablet shell may appear in your stool. This is a normal side effect and will not make the medication less effective.

Your blood sugar will need to be checked often, and you may need other blood tests at your doctor’s office.

Low blood sugar (hypoglycemia) can happen to everyone who has diabetes. Symptoms include headache, hunger, sweating, irritability, dizziness, nausea, fast heart rate, and feeling anxious or shaky. To quickly treat low blood sugar, always keep a fast-acting source of sugar with you such as fruit juice, hard candy, crackers, raisins, or non-diet soda.

Your doctor can prescribe a glucagon emergency injection kit to use in case you have severe hypoglycemia and cannot eat or drink. Be sure your family and close friends know how to give you this injection in an emergency.

Blood sugar levels can be affected by stress, illness, surgery, exercise, alcohol use, or skipping meals. Ask your doctor before changing your dose or medication schedule.

Metformin is only part of a complete treatment program that may also include diet, exercise, weight control, and special medical care. Follow your doctor’s instructions very closely.