Do NOT use Metformin if:

• you are allergic to any ingredient in Metformin
• you have congestive heart failure that is treated by medicine
• you have a severe infection, low blood oxygen levels, kidney or liver problems, high blood ketone or acid levels (eg, diabetic ketoacidosis), or severe dehydration
• you have had a stroke or a recent heart attack, or you are in shock
• you are 80 years old or older and have not had a kidney function test
• you will be having surgery or certain lab procedures.

Contact your doctor or health care provider right away if any of these apply to you.

Some medical conditions may interact with Metformin. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

• if you are pregnant, planning to become pregnant, or are breast-feeding
• if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
• if you have allergies to medicines, foods, or other substances
• if you have a history of heart problems (eg, heart failure), lung or breathing problems, thyroid problems, stomach or bowel problems (eg, paralysis, blockage), adrenal or pituitary problems, or lactic acidosis
• if you have vomiting, diarrhea, poor health or nutrition, low blood calcium or vitamin B₁₂ levels, or anemia, or if you are dehydrated
• if you have an infection, fever, recent injury, or moderate to severe burns
• if you drink alcohol or have a history of alcohol abuse
• if you will be having surgery or certain lab procedures
• if you take a beta-blocker (eg, propranolol).

Some medicines may interact with Metformin. Tell your health care provider if you are taking any other medicines, especially any of the following:

• Amiloride, cimetidine, digoxin, morphine, procainamide, quinidine, quinine, ranitidine, triamterene, trimethoprim, or vancomycin because they may increase the risk of Metformin's side effects
• Calcium channel blockers (eg, nifedipine), corticosteroids (eg, prednisone), diuretics (eg, furosemide, hydrochlorothiazide), estrogen, hormonal contraceptives (eg, birth control pills), insulin, isoniazid, nicotinic acid, phenothiazine (eg, chlorpromazine), phenytoin, sulfonylureas (eg, glipizide), sympathomimetics (eg, albuterol, pseudoephedrine), or thyroid hormones (eg, levothyroxine) because the risk of high or low blood sugar may be increased.

This may not be a complete list of all interactions that may occur. Ask your health care provider if Metformin may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

Important safety information:

• Dizziness may occur while you are taking Metformin. This effect may be worse if you take it with alcohol or certain medicines. Use Metformin with caution. Do not drive or perform other possible unsafe tasks until you know how you react to it.
• Follow the diet and exercise program given to you by your health care provider.
• Do not drink large amounts of alcohol while you use Metformin. Talk to your doctor or health care provider before you drink alcohol while you use Metformin.
• Tell your doctor or dentist that you take Metformin before you receive any medical or dental care, emergency care, or surgery.
• Be careful not to become dehydrated, especially during hot weather or while you are being active. Dehydration may increase the risk of Metformin's side effects.
• If vomiting or diarrhea occurs, you will need to take care not to become dehydrated. Contact your doctor for instructions.
• Carry an ID card at all times that says you have diabetes. Check your blood sugar levels as directed by your doctor. If they are often higher or lower than they should be and you take Metformin exactly as prescribed, tell your doctor.
• Metformin does not usually cause low blood sugar. Low blood sugar may be more likely to occur if you skip a meal, exercise heavily, or drink alcohol. It may also be more likely if you take Metformin along with certain medicines for diabetes (eg, sulfonylureas, insulin). It is a good idea to carry a reliable source of glucose (eg, tablets or gel) to treat low blood sugar. If this is not available, you should eat or drink a quick source of sugar like table sugar, honey, candy, orange juice, or non-diet soda. This will raise your blood sugar level quickly. Tell your doctor right away if this happens. To prevent low blood sugar, eat meals at the same time each day and do not skip meals.
• Fever, infection, injury, or surgery may increase your risk for high or low blood sugar levels. If any of these occur, check your blood sugar closely and tell your doctor right away.
• Metformin may commonly cause stomach upset, indigestion, nausea, vomiting, or diarrhea at the beginning of treatment. If you develop unusual or unexpected stomach problems, or if you develop stomach problems later during treatment, contact your doctor at once. This may be a sign of lactic acidosis.
• Lab tests, including kidney function, fasting blood glucose, hemoglobin A_1c, and blood counts, may be performed while you use Metformin. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
• Use Metformin with caution in the elderly; they may be more sensitive to its effects. Low blood sugar levels may also be more difficult to recognize in the elderly.
• Metformin should not be used in children younger 10 years; safety and effectiveness in these children have not been confirmed.
• Pregnancy and breast-feeding: If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using Metformin while you are pregnant. It is not known if Metformin is found in breast milk. Do not breastfeed while taking Metformin.

When used for long periods of time, Metformin may not work as well. If your blood sugar has been under control and then becomes hard to manage, contact your doctor. Do not change the dose of your medicine without checking with your doctor.

All medicines may cause side effects, but many people have no, or minor, side effects.

Check with your doctor if any of these most common side effects persist or become bothersome:

Diarrhea; gas; headache; indigestion; nausea; stomach upset; temporary metallic taste; vomiting.

Seek medical attention right away if any of these severe side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); chest pain or discomfort; dizziness or lightheadedness; fast or difficult breathing; feeling of being unusually cold; fever, chills, or persistent sore throat; general feeling of being unwell; muscle pain or weakness; slow or irregular heartbeat; unusual drowsiness; unusual or persistent stomach pain or discomfort; unusual tiredness or weakness.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider.