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Drug Profile

The information on this site is intended to supplement and enhance, not replace, the advice of a physician who is familiar with your medical history. Decisions about your health should always be made ONLY after detailed conversation with your doctor.

Limited Use [what does this mean?]
Generic drug name: metformin (met FOR min)
Brand name(s): FORTAMET, GLUCOPHAGE, GLUCOPHAGE XR, GLUMETZA, RIOMET
GENERIC: available FAMILY: Biguanides
Find the drug label by searching at DailyMed.

Pregnancy and Breast-feeding Warnings [top]

Pregnancy Warning

No valid data are available for metformin. Many experts recommend that insulin be used during pregnancy to maintain blood glucose levels. Tell your doctor if you are pregnant or thinking of becoming pregnant before you use this drug.

Breast-feeding Warning

Metformin is excreted in animal milk. It is likely that this drug, like many others, is also excreted in human milk and, because of the potential for serious adverse effects in nursing infants, you should not take this drug while nursing.

Safety Warnings For This Drug [top]

FDA-REQUIRED BLACK-BOX WARNING*

Metformin can cause lactic acidosis (a buildup of lactic acid in the blood), which can cause hypothermia (low body temperature), hypotension (low blood pressure), an abnormally slow heart rate and death. The onset of metformin-associated lactic acidosis is often subtle, accompanied only by nonspecific symptoms such as malaise (a general feeling of discomfort or being unwell), muscle aches, difficulty breathing, sleepiness and abdominal pain. This condition is diagnosed by blood tests, including a high blood lactate level.

Risk factors for metformin-associated lactic acidosis include kidney impairment, concomitant use of certain drugs (for example, carbonic anhydrase inhibitors such as topiramate [QSYMIA, QUDEXY XR, TOPAMAX, TROKENDI XR]), age 65 years old or older, having a radiological study with intravenous contrast, surgery and other procedures, conditions that cause low blood oxygen levels (for example, acute congestive heart failure), excessive alcohol intake and impaired liver function.

In patients suspected of having metformin-associated lactic acidosis, the drug should be immediately discontinued and general supportive measures should be instituted in a hospital setting. Prompt hemodialysis treatment also is recommended.

*This warning is paraphrased from the FDA-approved drug labeling.

Facts About This Drug [top]

Metformin (GLUCOPHAGE, GLUCOPHAGE XR, GLUMETZA, RIOMET) was approved by the Food and Drug Administration (FDA) in 1995 for use in combination with diet and exercise to control blood sugar in adults and children with type 2 diabetes. It is the only FDA-approved drug that belongs to the biguanide family of drugs — a group of oral type 2 diabetes drugs that work by preventing the production of glucose by the liver, improving the body’s sensitivity towards insulin and reducing the amount of sugar...

Metformin (GLUCOPHAGE, GLUCOPHAGE XR, GLUMETZA, RIOMET) was approved by the Food and Drug Administration (FDA) in 1995 for use in combination with diet and exercise to control blood sugar in adults and children with type 2 diabetes. It is the only FDA-approved drug that belongs to the biguanide family of drugs — a group of oral type 2 diabetes drugs that work by preventing the production of glucose by the liver, improving the body’s sensitivity towards insulin and reducing the amount of sugar absorbed by the intestines.[1]

Metformin is the drug of choice for initial treatment of patients with type 2 diabetes who are not able to control their blood sugar through diet and exercise alone and who do not have severe kidney impairment.[2],[3],[4] One of the most effective drugs for lowering blood sugar, metformin does not cause weight gain, rarely causes hypoglycemia, has few adverse effects and is available in generic versions at low cost.[4]

For patients who fail to achieve adequate lowering of their blood hemoglobin A1c level (a measure of blood sugar control over the preceding two to three months) with metformin alone, adding a second- or third-generation sulfonylurea, such as glyburide (DIABETA, GLYNASE) or glipizide (GLUCOTROL), may be appropriate.[2]

Public Citizen’s Health Research Group has designated metformin as Limited Use because it can cause lactic acidosis (a buildup of lactic acid in the blood) and should not be used in patients with severe kidney impairment because they are at greatest risk of this rare but potentially fatal adverse reaction (see FDA-required black-box warning above).

Over the past two decades, many fixed-dose combination medications containing metformin and another oral diabetes drug have been marketed in the U.S. We have designated all of these combinations as Do Not Use.

The United Kingdom Prospective Diabetes Study (UKPDS), which was published in The Lancet in 1998, included a randomized clinical trial that compared use of metformin with conventional treatment (primarily diet alone) in more than 750 overweight subjects with newly diagnosed type 2 diabetes.[5] The UKPDS researchers found that metformin treatment resulted in improved survival and a reduction in cardiovascular complications. Specifically, after an average follow-up of more than 10 years, subjects in the metformin group had a 36% lower risk of death from any cause than did subjects in the diet group. Subjects receiving metformin also had a 30% lower risk of adverse cardiovascular events (heart attack, sudden death, chest pain from coronary artery disease, stroke and peripheral vascular disease) than did those in the diet group.

Adverse effects

Although recommended as the first-choice drug among all oral diabetes drugs, metformin very rarely can cause lactic acidosis,[6] which is estimated to be fatal in about 50% of cases. The increased risk of lactic acidosis is the reason that the FDA required a black-box warning — the strongest type of warning that the FDA can require — in the drug’s product labeling.

Metformin should never be taken by patients with severe kidney impairment because they are at greatest risk of this adverse effect. The drug also should be avoided in patients with liver disease and used with caution in patients with any other risk factors for metformin-associated lactic acidosis, including heart failure.

The FDA initially required that the product labeling warn against the use of metformin in patients with any degree of kidney impairment.[7] However, in 2016, the agency announced that it had concluded that metformin can be used safely in patients with mild kidney impairment and in some patients with moderate kidney impairment. Therefore, the agency required changes to the product labeling for metformin to reflect this conclusion.

Before starting metformin, make sure your doctor does a blood test to measure your kidney function. If you have advanced moderate or severe kidney impairment, you should not start taking metformin. When using metformin, your doctor should check your kidney function periodically. If you develop severe kidney impairment while taking the drug, you should be switched to another diabetes drug, such as a second- or third-generation sulfonylurea or insulin.

Metformin also can reduce the intestinal absorption of vitamin B12 from ingested food. Long-term use of metformin may result in vitamin B12 deficiency, which can lead to anemia and neurologic symptoms, including problems with cognitive function.[8]

In April 2017, the FDA updated the product label for metformin to indicate that liver injury has been reported with metformin use.

Before You Use This Drug [top]

Do not use except in special situations if you have or have had:

  • severe burns
  • dehydration
  • diabetic coma
  • diabetic ketoacidosis
  • hyperosmolar nonketotic coma
  • severe infection
  • major surgery
  • severe trauma
  • cardiorespiratory insufficiency
  • cardiovascular collapse
  • congestive heart failure
  • heart attack
  • liver disease
  • lactic acidosis
  • kidney disease or poor kidney function
  • diagnostic or medical procedures using IV contrast media containing iodine

Tell your doctor if you have or have had:

  • allergies to drugs
  • pregnancy or are breast-feeding
  • diarrhea
  • gastroparesis
  • intestinal blockage
  • vomiting
  • conditions causing delayed food absorption
  • female hormonal changes
  • high fever
  • high levels of cortisol
  • hyperthyroidism
  • adrenal insufficiency
  • pituitary insufficiency
  • hypothyroidism

Tell your doctor about any other drugs you take, including aspirin, herbs, vitamins and other nonprescription drugs.

When You Use This Drug [top]

  • Call your doctor immediately and eat or drink something with sugar in it if you experience the symptoms of low blood sugar.
  • Call your doctor immediately if you experience the symptoms of lactic acidosis.

How to Use This Drug [top]

  • If you miss a dose, take it as soon as you remember, but skip it if it is almost time for the next dose. Do not take double doses.
  • Store between 59 degrees Farenheit and 86 degrees Farenheit in a light-resistant container, unless otherwise specified by the manufacturer.

Interactions with Other Drugs [top]

The following drugs, biologics (e.g., vaccines, therapeutic antibodies), or foods are listed in Evaluations of Drug Interactions 2003 as causing “highly clinically significant” or “clinically significant” interactions when used together with any of the drugs in this section. In some sections with multiple drugs, the interaction may have been reported for one but not all drugs in this section, but we include the interaction because the drugs in this section are similar to one another. We have also included potentially serious interactions listed in the drug’s FDA-approved professional package insert or in published medical journal articles. There may be other drugs, especially those in the families of drugs listed below, that also will react with this drug to cause severe adverse effects. Make sure to tell your doctor and pharmacist the drugs you are taking and tell them if you are taking any of these interacting drugs:

Metformin should be temporarily discontinued if you are undergoing a radiologic procedure that requires the use of an intravenous contrast product containing iodine.

The thiazide diuretics, or water pills, interact with metformin.

Other drugs that interact with metformin are: acetophenazine, ACTH, ADDERAL, ADVIR, AEROBID, albuterol, ALUPENT, amiloride, amlodipine, ARAMINE, ARMOUR THYROID, BACTRIM, beclomethasone, BECLOVENT, benzphetamine, bepridil, bitolterol, BRONKOSOL, CALAN, CARDENE, CARDIZEM, chloral hydrate, chlorpromazine, CHOLOXIN, cimetidine, COMPAZINE, corticotropin, cortisone, cosyntropin, COTROSYN, COVERA, DECADRON, DEPO-MEDROL, desoxycorticosterone, DEXADRINE, dexamethasone, dextroamphetamine, dextrothyroxine, DIDREX, diethylpropion, digoxin, DILACOR, DILANTIN, diltiazem, DIULO, dobutamine, DOBUTREX, DOCA, dofetilide, dopamine, DYNACIRC, DYRENIUM, ephedrine, epinephrine, ETRAFON, FASTIN, felodipine, flunisolide, fluphenazine, furosemide, hydrocortisone, indapamide, INH, isoetharine, isoniazid, isoproterenol, isradipine, ISUPRIL, LANOXIN, LASIX, levothyroxine, LOZOL, MAXIR, mazindol, MEDROL, mephentermine, mesoridazine, metaproterenol, metaraminol, methamphetamine, methdilazine, methylphenidate, methylprednisolone, metolazone, MIDAMOR, midodrine, morphine, NASALIDE, nicardipine, nimodipine, NIMOTOP, nisoldipine, NOCTEC, norepinephrine, NORVASC, oral contraceptives, orlistat, PERMITIL, perphenazine, PHENERGAN, phenmetrazine, phentermine, phenylephrine, phenytoin, piperacetazine, pirbuterol, PLENDIL, PRELUDIN, PROAMATINE, procainamide, PROCANBID, prochlorperazine, promethazine, PROVENTIL, pseudoephedrine, QUIDE, QUINAGLUTE, QUINIDEX, quinidine, quinine, ranitadine, RITALIN, ritodrine, salmeterol, SANOREX, SEREVENT, SERENTIL, STELAZINE, SUDAFED, SULAR, sulfamethoxazone-trimethoprim, SYNTHROID, TACRYL, TAGAMET, TENUATE, THORAZINE, thyroid, TIAZAC, TIKOSYN, TINDAL, TORNALATE, triameterene, trifluoperazine, VANCENASE, VANCERIL, VASCOR, verapamil, WYAMINE, XENICAL, YUTOPAR, ZANTAC.

Adverse Effects [top]

Call your doctor immediately if you experience:

  • tiredness and/or weakness
  • signs of low blood sugar: anxiety, blurred vision, cold sweats or cool, pale skin, confusion, difficulty concentrating, drowsiness, increased hunger, headache, nausea, nervousness, nightmares and restless sleep, rapid heartbeat, shakiness, slurred speech, unsteady walk, abnormal tiredness or weakness, behavior change similar to drunkenness, weight gain
  • signs of high blood sugar: blurred vision, drowsiness, dry, flushed skin, breath smells of fruit, increased urination, loss of appetite, tiredness, abnormal thirst, deep, rapid breathing, dizziness, dry mouth, headache, stomachache, nausea, vomiting
  • lactic acidosis

Call your doctor if these symptoms continue:

  • loss of appetite
  • diarrhea
  • upset stomach
  • passing of gas
  • headache
  • metallic taste
  • nausea
  • vomiting
  • weight loss

Periodic Tests[top]

Ask your doctor which of these tests should be done periodically while you are taking this drug and how often they should be done:

  • folic acid and vitamin B12 levels
  • blood sugar levels
  • glycosylated hemoglobin (hemoglobin A1c) levels
  • routine blood tests
  • regular physical examinations
  • kidney function tests

last reviewed June 30, 2021