Part Two of Metformin Information, Focusing on Side Effects, Discontinuation or Withdrawal Effects, and Additional Information

This second section of our medication database entry focuses on potential side effects, withdrawal or discontinuation effects, and additional information, while part one covers basic drug characteristics, uses and benefits.

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What are the possible side effects of metformin?

  • Stop taking metformin and seek emergency medical attention if you experience an allergic reaction (difficulty breathing; closing of your throat; swelling of your lips, tongue, or face; or hives).
  • A small number of people who have taken metformin have developed a serious condition called lactic acidosis that has been fatal in up to 50% of cases. Lactic acidosis has occurred most often in people whose kidneys were not working properly. Liver problems may also increase the risk of developing lactic acidosis. Stop taking metformin and call your doctor immediately if you experience a feeling of general discomfort or sickness; weakness; sore or aching muscles; trouble breathing, unusual drowsiness, dizziness or lightheadedness; unusual or unexplained stomach upset (after the initial stomach upset that may occur at the start of therapy with metformin); or the sudden development of a slow or irregular heartbeat. These may be signs of lactic acidosis.
  • Other, less serious side effects may be more likely to occur. Continue to take metformin and talk to your doctor if you experience
    • nausea, vomiting, abdominal pain, or diarrhea at the start of therapy;
    • abdominal bloating or increased gas production; or
    • decreased appetite or changes in taste (metallic taste in your mouth).
  • Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

What other drugs will affect metformin?

  • Before taking this medication, tell your doctor if you are taking any of the following medications:
    • a diuretic (water pill) such as furosemide (Lasix), bumetanide (Bumex), ethacrynic acid (Edecrin), torsemide (Demadex), amiloride (Midamor), triamterene (Dyazide, Maxzide, Dyrenium), spironolactone (Aldactone), hydrochlorothiazide (HydroDiuril), chlorothiazide (Diuril), chlorthalidone (Hygroton), indapamide (Lozol), metolazone (Zaroxolyn, Mykrox), and others;
    • a phenothiazine such as chlorpromazine (Thorazine), prochlorperazine (Compazine), promethazine (Phenergan), and others
    • an estrogen (Premarin, Prempro, Ogen, and others) or birth control pill (Ovral, Lo-Ovral, Ortho-Novum, Triphasil, Levlen, Tri-Levlen, Alesse, and others)
    • a calcium channel blocker such as nifedipine (Adalat, Procardia), verapamil (Calan, Verelan, Isoptin), diltiazem (Cardizem, Dilacor XR), felodipine (Plendil), bepridil (Vascor), amlodipine (Norvasc), and others;
    • a steroid medication such as prednisone (Deltasone), methylprednisolone (Medrol), dexamethasone (Decadron), and others;
    • a thyroid medication (Synthroid, Levoxyl, Levothroid, and others),
    • digoxin (Lanoxin, Lanoxicaps);
    • procainamide (Pronestyl);
    • quinidine (Cardioquin, others);
    • cimetidine (Tagamet, Tagamet HB) or ranitidine (Zantac, Zantac 75);
    • morphine (Astramorph, MS Contin, Roxanol, and others);
    • trimethoprim (Proloprim, Trimpex, Septra, Bactrim);
    • phenytoin (Dilantin);
    • isoniazid (Nydrazid); or
    • nicotinic acid or niacin (Nicobid, Nicolar, others).
  • You may not be able to take metformin, or you may require a dosage adjustment or special monitoring if you are taking any of the medicines listed above.
  • Drugs other than those listed here may also interact with metformin or affect your condition. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines.

Where can I get more information?

  • Your pharmacist has more information about metformin written for health professionals that you may read.
  • Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Limitations and the Source of Our Online Medication Information Database

Although we have made considerable efforts to ensure that the information provided here is accurate, up-to-date, and complete, MedLibrary.org makes no guarantee to that effect. Drug information contained herein may be time sensitive. This medication information does not endorse drugs, diagnose patients or recommend any specific pharmacotherapy. This is an educational resource only -- intended to supplement but not to replace the expertise, skill, knowledge and judgment of medically qualified healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, please check with your doctor, nurse or local pharmacist. MedLibrary.org does not assume any responsibility for any aspect of healthcare administered with the aid of information provided here.

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Version: 5.07. Revision Date: 2/14/03.

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