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Generic Name:

metformin, Oral tablet

All Brands

  • Glucophage
SECTION 1 of 5

Highlights for metformin

Oral tablet
1

Metformin is an oral drug used to treat high blood sugar levels caused by type 2 diabetes.

2

Not managing your diabetes well can harm your heart, kidneys, nerves, and eyes. Taking diabetes drugs like metformin and making healthy lifestyle changes can lower your risk of these issues. Lifestyle changes include good nutrition, regular exercise, and not smoking.

3

Lactic acidosis is a rare side effect of metformin that can be fatal. In this condition, lactic acid builds up in your blood. This is a medical emergency that requires treatment in the hospital.

4

Avoid drinking alcohol while taking metformin. Alcohol can lower or raise your blood sugar levels. Alcohol use may also increase your risk of lactic acidosis.

5

Common side effects include nausea, vomiting, stomach pain, and diarrhea. Taking this medication with food may lower your risk of having side effects.

IMPORTANT INFORMATION

FDA warning

This drug has a Black Box Warning. This is the most serious warning from the Food and Drug Administration (FDA). A black box warning alerts doctors and patients to potentially dangerous effects. 

Lactic acidosis warning: Lactic acidosis is a rare but serious side effect of this drug. In this condition, lactic acid builds up in your blood. This is a medical emergency that requires treatment in the hospital. Lactic acidosis is fatal in about half of people who develop it. You should stop taking this drug and call your doctor right away or go to the emergency room if you have signs of lactic acidosis. Symptoms include:

  • tiredness
  • weakness
  • unusual muscle pain
  • trouble breathing
  • unusual sleepiness
  • stomach pains, nausea, or vomiting
  • dizziness or lightheadedness
  • slow or irregular heart rate

Alcohol use

You shouldn’t drink alcohol while taking this drug. Alcohol can affect your blood sugar levels unpredictably and increase your risk of lactic acidosis.

Kidney problems

If you have moderate to severe kidney problems, you have a higher risk of lactic acidosis. You shouldn’t take this drug.

Liver problems

Liver disease is a risk factor for lactic acidosis. You shouldn’t take this drug if you have liver problems.

What is metformin?

This drug is a prescription drug. It’s available in these forms: oral immediate-release tablet and oral extended-release tablet.

This drug is available as a generic drug. Generic drugs usually cost less. In some cases they may not be available in every strength or form as the brand. Talk to your healthcare provider to see if the generic will work for you.

This drug may be used as part of a combination therapy. That means you need to take it with other drugs.

Why it's used

This drug is used to treat high blood sugar levels caused by type 2 diabetes. It works along with diet and exercise.

How it works

This drug belongs to a class of drugs called biguanides. A class of drugs refers to medications that work similarly.

More Details

How it works

This drug belongs to a class of drugs called biguanides. A class of drugs refers to medications that work similarly. They have a similar chemical structure and are often used to treat similar conditions.

This drug reduces the amount of glucose (sugar) made by your liver, lowers the amount of glucose your body absorbs, and increases the effect of insulin on your body. Insulin is a hormone that helps your body remove extra sugar from your blood. This lowers your blood sugar levels.

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SECTION 2 of 5

metformin Side Effects

Oral tablet

More Common Side Effects

The more common side effects that occur with metformin include:

  • stomach problems:

    • diarrhea
    • nausea
    • stomach pain
    • heartburn
    • gas

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious Side Effects

If you experience any of these serious side effects, call your doctor right away. If your symptoms are potentially life-threatening, or if you think you’re experiencing a medical emergency, call 9-1-1.

  • lactic acidosis. Symptoms include:

    • tiredness
    • weakness
    • unusual muscle pain
    • trouble breathing
    • unusual sleepiness
    • stomach pains, nausea, or vomiting
    • dizziness or lightheadedness
    • slow or irregular heart rate
  • low blood sugar. Symptoms include:

    • headache
    • weakness
    • confusion
    • shaking or feeling jittery
    • drowsiness
    • dizziness
    • irritability
    • sweating
    • hunger
    • fast heart rate
Pharmacist's Advice
Clinical Associate Professor, University of Illinois at Chicago College of Pharmacy

This drug does not cause drowsiness. However, it may cause a low blood sugar reaction.

If you have a low blood sugar reaction, you need to treat it.

  • For mild hypoglycemia (55–70 mg/dL), treatment is 15–20 grams of glucose (a type of sugar). You need to eat or drink one of the following:
    • 3–4 glucose tablets
    • a tube of glucose gel
    • ½ cup of juice or regular, non-diet soda
    • 1 cup of nonfat or 1% cow’s milk
    • 1 tablespoon of sugar, honey, or corn syrup
    • 8–10 pieces of hard candy, such as lifesavers
  • Test your blood sugar 15 minutes after you treat the low sugar reaction. If your blood sugar is still low, then repeat the above treatment.
  • Once your blood sugar is back in the normal range, eat a small snack if your next planned meal or snack is more than 1 hour later. 

If you don’t treat low blood sugar, you can have a seizure, pass out, and possibly develop brain damage. Low blood sugar can even be fatal. If you pass out because of a low sugar reaction or cannot swallow, someone will have to give you an injection of glucagon to treat the low sugar reaction. You may need to go to the emergency room.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.
SECTION 3 of 5

metformin May Interact with Other Medications

Oral tablet

Metformin can interact with other medications, herbs, or vitamins you might be taking. That’s why your doctor should manage all of your medications carefully. If you’re curious about how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Note: You can reduce your chances of drug interactions by having all of your prescriptions filled at the same pharmacy. That way, a pharmacist can check for possible drug interactions.

Alcohol interaction

The use of drinks that contain alcohol can increase your risk of lactic acidosis from metformin. Alcohol may also raise or lower your blood sugar levels. If you drink alcohol, talk to your doctor. 

Medications that might interact with this drug

Diabetes drugs

Using these drugs with metformin can cause low blood sugar levels. Your doctor may reduce your dose of your other diabetes medications if you start taking metformin.

These drugs include:

  • insulin
  • medications that release insulin

Heart or blood pressure drugs

These drugs may reduce the effectiveness of metformin. This means that it won’t work to treat your diabetes. 

These drugs include:

  • diuretics
  • calcium channel blockers, such as nifedipine

Heart rhythm problem drugs

Metformin may increase the levels of these medications in your body. This raises your risk of side effects.

These drugs include:

  • digoxin
  • procainamide
  • quinidine

Cholesterol drugs

These drugs may make metformin less effective in lowering your blood sugar.

These drugs include:

  • nicotinic acid

Glaucoma drugs

Using these drugs with metformin may increase your risk of lactic acidosis.

These drugs include:

  • acetazolamide
  • brinzolamide
  • dorzolamide
  • methazolamide

Topiramate

Using this drug with metformin may increase your risk of lactic acidosis. You shouldn’t use these medications together.

Phenytoin

This drug may make metformin less effective in lowering your blood sugar.

Antibiotics

Metformin may increase the levels of these medications in your body. This raises your risk of side effects.

These drugs include:

  • trimethoprim
  • vancomycin

Stomach problems drugs

Metformin may increase the levels of these medications in your body. This raises your risk of side effects.

These drugs include:

  • cimetidine
  • ranitidine

Phenothiazines

These drugs may make metformin less effective in lowering your blood sugar.

Pain medications

Metformin may increase the levels of these medications in your body. This raises your risk of side effects. 

These drugs include:

  • morphine

Malaria drugs

Metformin may increase the levels of these medications in your body. This raises your risk of side effects.

These drugs include:

  • quinine

Hormone drugs

These drugs may make metformin less effective in lowering your blood sugar.

These drugs include:

  • corticosteroids (inhaled and oral)

Tuberculosis drugs

These drugs may make metformin less effective in lowering your blood sugar. 

These drugs include:

  • isoniazid

Thyroid drugs

These drugs may make metformin less effective in lowering your blood sugar.

These drugs include:

  • dessicated thyroid
  • levothyroxine
  • liothyronine
  • liotrix

Estrogens

These drugs may make metformin less effective in lowering your blood sugar.

These drugs include:

  • conjugated estrogens
  • estradiol

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.
Drug warnings
kidney problems
People with kidney problems

If you have moderate to severe kidney problems, you have a higher risk of lactic acidosis. You shouldn’t take this drug.

liver problems
People with liver problems

Liver disease is a risk factor for lactic acidosis. You shouldn’t take this drug if you have liver problems.

x-ray procedure
People who plan to have an x-ray procedure

You’ll need to stop taking this drug for a short time if you plan to have an injection of dye or contrast for an x-ray procedure. This can affect how your kidneys work and put you at risk for lactic acidosis.

plans to have surgery
People with illnesses or plans to have surgery

Tell your doctor if you have a fever or infection, are injured, or plan to have surgery or another medical procedure. They may need to change your dose of this drug.

diabetic ketoacidosis
People with diabetic ketoacidosis

You shouldn’t use this drug to treat diabetic ketoacidosis.

type 1 diabetes
People with type 1 diabetes

You shouldn’t use this drug to treat type 1 diabetes.

Pregnant women
Pregnant women

This drug is a pregnancy category B drug. That means two things:

  1. Research in animals has not shown a risk to the fetus when the mother takes the drug.
  2. There aren’t enough studies done in humans to show if the drug poses a risk to the fetus. 

Talk to your doctor if you’re pregnant or planning to become pregnant. Animal studies do not always predict the way humans would respond. Therefore, this drug should only be used in pregnancy if clearly needed.

breast-feeding
Women who are breast-feeding

This drug may pass into breast milk and may cause side effects in a child who is breast-fed.

Talk to your doctor if you breast-feed your baby. You may need to decide whether to stop breast-feeding or stop taking this medication.

seniors
For seniors

People 80 years of age and older shouldn’t start taking this drug unless they have normal kidney function. You have a higher risk of lactic acidosis. If you’re over 80 years of age and taking this drug, you shouldn’t take the maximum dose.

children
For children

The safety and effectiveness of this drug in people younger than 10 years hasn’t been established.

allergies
Allergies

This drug can cause a severe allergic reaction. Symptoms include:

  • trouble breathing
  • swelling of your throat or tongue
  • hives

Call 9-1-1 or go to the nearest emergency room if you develop these symptoms. 

Don’t take this drug again if you’ve ever had an allergic reaction to it before. Taking it again could be fatal (cause death).

SECTION 4 of 5

How to Take metformin (Dosage)

Oral tablet

All possible dosages and forms may not be included here. Your dose, form, and how often you take it will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

What are you taking this medication for?

Type 2 diabetes

Brand: Glucophage

Form: Oral immediate-release tablet
Strengths: 500 mg, 850 mg, 1000 mg

Brand: Glucophage XR

Form: Oral extended-release tablet
Strengths: 500 mg, 750 mg

Brand: Riomet

Form: Oral solution
Strengths: 500 mg/5 mL

Brand: Fortamet

Form: Oral extended-release tablet
Strengths: 500 mg, 1000 mg

Brand: Glumetza

Form: Oral extended-release tablet
Strengths: 500 mg, 1000 mg

Generic: metformin

Form: Oral immediate-release tablet
Strengths: 500 mg, 850 mg, 1000 mg
Form: Oral extended-release tablet
Strengths: 500 mg, 750 mg, 1000 mg
Adult dosage (ages 18–79 years)
  • immediate-release tablets and oral solution:
    • Starting dose: 500–800 mg or 5–8.5 mL per day taken with meals.
    • When changing your dose:
      • Your doctor will increase your dose by 500–850 mg or 5–8.5 mL every 1–2 weeks, up to a total of 2,000 mg or 20 mL taken per day in two doses. 
      • If your doctor gives you a dose greater than 2,000 mg or 20 mL per day, you may have to take the medication three times per day.
      • The maximum dose is 2,550 mg or 25.5 mL per day.
  • extended-release tablets:
    • Starting dose: 500 mg taken once per day with your evening meal. The usual starting dose for Glumetza is 1,000 mg taken once per day with your evening meal. The usual starting dose for Fortamet is 500–1000 mg taken once per day with your evening meal.
    • When changing your dose:
      • Your doctor will increase your dose by 500 mg every week, up to a maximum of 2,000 mg per day. (The maximum dose of Fortamet is 2,500 mg per day.)
      • Your doctor may have you take 1,000 mg two times per day for better control of your blood sugar.
Child dosage (ages 10–17 years)
  • immediate-release tablets and oral solution:
    • Starting dose: 500 mg or 5 mL taken twice per day.
    • When changing your dose:
      • Your doctor will increase your dose by 500 mg or 5 mL every week in divided doses.
      • The maximum dose is 2,000 mg or 20 mL per day.
  • extended-release tablets: This medication hasn’t been studied in children younger than 10 years of age and should not be used.
Child dosage (ages 0–9 years)

This medication hasn’t been studied in children younger than 10 years of age and shouldn’t be used.

Senior dosage (ages 80 years and older)

People 80 years of age and older shouldn’t start taking metformin unless they have normal kidney function. You have a higher risk of lactic acidosis. If you’re over 80 years of age and taking metformin, you shouldn’t take the maximum dose.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.
Pharmacist's Advice
Clinical Associate Professor, University of Illinois at Chicago College of Pharmacy

This drug comes with serious risks if you don’t take it as prescribed.

If you don't take it at all

Your symptoms of type 2 diabetes may not improve or may even get worse over time.

If you stop taking it suddenly

If your condition improved while taking this medication regularly and you stop taking it, your symptoms of type 2 diabetes may come back.

If you don't take it on schedule

You may not see the full benefit of this medication.

If you take too much

You could have dangerous levels of the drug in your body. You may have the following symptoms:

  • stomach pain
  • nausea
  • vomiting
  • diarrhea
  • drowsiness
  • headache
  • lactic acidosis

If you think you’ve taken too much of the drug, act right away. Call your doctor or local poison control center, or go to the nearest emergency room.

What to do if you miss a dose

If you forget to take your dose, take it as soon as you remember. If it’s just a few hours before the time for your next dose, then only take one dose at that time.

Never try to catch up by taking two doses at once. This could result in toxic side effects.

How to tell if the drug is working

You may be able to tell if this drug is working if your blood sugar is near your target range as decided by your doctor. Your symptoms of diabetes may also get better.

This drug is used for long-term treatment.

The extended-release tablets shouldn’t be crushed or cut

The regular oral tablets may be split or crushed.

Store this drug at room temperature

  • Keep it between 68°F and 77°F (20°C and 25°C). This medication can be stored briefly between 59°F and 86°F (15°C and 30°C).
  • Keep this drug away from light.
  • Keep it away from high temperatures.
  • Keep your drugs away from areas where they could get wet, such as bathrooms. Store this drug away from moisture and damp locations.

Travel

When traveling with your medication:

  • Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag.
  • Don’t worry about airport x-ray machines. They can’t hurt your medication.
  • You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled box with you.
  • Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.

Self-management

Your doctor may have you regularly test your blood sugar levels at home.

If your doctor decides that you need to test your blood sugar at home, you’ll need the following:

  • sterile alcohol wipes
  • lancing device and lancets (needles used to get drops of blood from your finger to test your blood sugar)
  • blood sugar test strips
  • blood glucose monitoring machine
  • needle container for safe disposal of lancets

Ask your doctor or pharmacist how to use your blood glucose monitoring machine. You need to know how to use this device to test your blood sugar. 

Clinical monitoring

Before starting and during your treatment with this drug, your doctor may check your:

  • blood sugar levels
  • glycosylated hemoglobin (A1C) levels. This test measures your blood sugar control over the last 2–3 months.
  • cholesterol
  • vitamin B12 levels
  • kidney function

Your diet

This drug, when combined with lifestyle changes (diet, exercise, and not smoking), can help lower your blood sugar. Follow the nutrition plan that your doctor, registered dietician, or diabetes educator recommends.

Hidden costs

If your doctor decides that you need to test your blood sugar at home, you’ll need the following:

  • sterile alcohol wipes
  • lancing device and lancets (needles used to get drops of blood from your finger to test your blood sugar)
  • blood sugar test strips
  • blood glucose monitoring machine
  • needle container for safe disposal of lancets

Are there any alternatives?

There are other drugs available to treat your condition. Some may be more suitable for you than others. Talk to your doctor about possible alternatives.

SECTION 5 of 5

How Much Does metformin Cost?

Oral tablet

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These prices represent the lowest priced national pharmacies for metformin on GoodRx. They may be lower than your insurance.

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Content developed in collaboration with University of Illinois-Chicago, Drug Information Group

Medically reviewed by Creighton University, Center for Drug Information and Evidence-Based Practice on October 26, 2015

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.
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