This information from Lexicomp® explains what you need to know about this medication, including what it’s used for, how to take it, its side effects, and when to call your healthcare provider.
- Rarely, metformin may cause too much lactic acid in the blood (lactic acidosis). The risk is higher in people who have kidney problems, liver problems, heart failure, use alcohol, or take other drugs like topiramate. The risk is also higher in people who are 65 or older and in people who are having surgery, an exam or test with contrast, or other procedures. If lactic acidosis happens, it can lead to other health problems and can be deadly. Kidney tests may be done while taking this drug.
- Do not take this drug if you have a very bad infection, low oxygen, or a lot of fluid loss (dehydration).
- Call your doctor right away if you have signs of too much lactic acid in the blood (lactic acidosis) like fast breathing, fast or slow heartbeat, a heartbeat that does not feel normal, very bad upset stomach or throwing up, feeling very sleepy, shortness of breath, feeling very tired or weak, very bad dizziness, feeling cold, or muscle pain or cramps.
- It is used to lower blood sugar in patients with high blood sugar (diabetes).
- If you are allergic to this drug; any part of this drug; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
- If you have type 1 diabetes. Do not use this drug to treat type 1 diabetes.
- If you have any of these health problems: Acidic blood problem, kidney disease, or liver disease.
- If you have had a recent heart attack or stroke.
- If you are not able to eat or drink like normal, including before certain procedures or surgery.
- If you are having an exam or test with contrast or have had one within the past 48 hours, talk with your doctor.
- If you are pregnant or may be pregnant. Do not take this drug if you are in the second or third trimester of pregnancy.
- If you are breast-feeding. Do not breast-feed while you take this drug.
This is not a list of all drugs or health problems that interact with this drug.
Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take this drug with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.
- Tell all of your health care providers that you take this drug. This includes your doctors, nurses, pharmacists, and dentists. This drug may need to be stopped before certain types of surgery as your doctor has told you. If this drug is stopped, your doctor will tell you when to start taking this drug again after your surgery or procedure.
- Talk with your doctor before you drink alcohol.
- Do not drive if your blood sugar has been low. There is a greater chance of you having a crash.
- To lower the chance of feeling dizzy or passing out, rise slowly if you have been sitting or lying down. Be careful going up and down stairs.
- Be careful in hot weather or while being active. Drink lots of fluids to stop fluid loss.
- If you are on a low-salt or salt-free diet, talk with your doctor.
- High cholesterol has happened with this drug. If you have questions, talk with the doctor.
- Have blood work checked as you have been told by the doctor. Talk with the doctor.
- This drug may affect certain lab tests. Tell all of your health care providers and lab workers that you take this drug.
- Check your blood sugar as you have been told by your doctor.
- Talk with your doctor about which glucose tests are best to use.
- Long-term treatment with metformin may lead to low vitamin B-12 levels. If you have ever had low vitamin B-12 levels, talk with your doctor.
- Too much acid in the blood or urine (ketoacidosis) and severe urinary tract infections (UTIs) have happened. Ketoacidosis can be deadly. Both of these may need to be treated in a hospital.
- It is common to have stomach problems like upset stomach, throwing up, or diarrhea when you start taking this drug. If you have stomach problems later during treatment, call your doctor right away. This may be a sign of an acid health problem in the blood (lactic acidosis).
- Kidney problems have happened. Sometimes, these may need to be treated in the hospital or with dialysis.
- This drug may raise the risk of lower limb amputations. Toe and foot amputations have happened most often. Talk to your doctor about how to take care of your feet. Tell your doctor if you have ever had an amputation, blood vessel disease, nerve disease, or a foot ulcer caused by diabetes. Call your doctor right away if you have new pain or tenderness, sores or ulcers, or infections in your legs or feet.
- A rare but very bad infection has happened with drugs like this one. This infection may be deadly. Get medical help right away if your genitals or the area between your genitals and rectum becomes tender, red, or swollen, and you have a fever or do not feel well.
- If you are 65 or older, use this drug with care. You could have more side effects.
- There is a chance of pregnancy in people of childbearing age who have not been ovulating. If you want to avoid pregnancy, use birth control while taking this drug.
- This drug may cause harm to the unborn baby if you take it while you are pregnant. If you are pregnant or you get pregnant while taking this drug, call your doctor right away.
WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:
- Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
- Signs of fluid and electrolyte problems like mood changes, confusion, muscle pain or weakness, fast or abnormal heartbeat, severe dizziness or passing out, increased thirst, seizures, feeling very tired or weak, decreased appetite, unable to pass urine or change in the amount of urine produced, dry mouth, dry eyes, or severe upset stomach or throwing up.
- Signs of too much acid in the blood (acidosis) like confusion; fast breathing; fast heartbeat; a heartbeat that does not feel normal; very bad stomach pain, upset stomach, or throwing up; feeling very sleepy; shortness of breath; or feeling very tired or weak.
- Signs of a urinary tract infection (UTI) like blood in the urine, burning or pain when passing urine, feeling the need to pass urine often or right away, fever, lower stomach pain, or pelvic pain.
- Signs of kidney problems like unable to pass urine, change in how much urine is passed, blood in the urine, or a big weight gain.
- Vaginal yeast infection. Report itching or discharge.
- Yeast infection of the penis. Report pain, swelling, rash, or discharge.
- Low blood sugar can happen. The chance may be raised when this drug is used with other drugs for diabetes. Signs may be dizziness, headache, feeling sleepy or weak, shaking, fast heartbeat, confusion, hunger, or sweating. Call your doctor right away if you have any of these signs. Follow what you have been told to do for low blood sugar. This may include taking glucose tablets, liquid glucose, or some fruit juices.
All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:
- Diarrhea, upset stomach, or throwing up.
- Stomach pain or heartburn.
- Feeling tired or weak.
These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.
You may report side effects to your national health agency.
Use this drug as ordered by your doctor. Read all information given to you. Follow all instructions closely.
- Take with meals.
- Keep taking this drug as you have been told by your doctor or other health care provider, even if you feel well.
- Drink lots of noncaffeine liquids unless told to drink less liquid by your doctor.
- Follow the diet and workout plan that your doctor told you about.
- It may be harder to control blood sugar during times of stress such as fever, infection, injury, or surgery. A change in physical activity, exercise, or diet may also affect blood sugar.
- If you cannot drink liquids by mouth or if you have upset stomach, throwing up, or diarrhea that does not go away; you need to avoid getting dehydrated. Contact your doctor to find out what to do. Dehydration may lead to low blood pressure or to new or worse kidney problems.
- Take a missed dose as soon as you think about it.
- If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
- Do not take 2 doses at the same time or extra doses.
- Store at room temperature in a dry place. Do not store in a bathroom.
- Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
- Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.
- If your symptoms or health problems do not get better or if they become worse, call your doctor.
- Do not share your drugs with others and do not take anyone else’s drugs.
- Some drugs may have another patient information leaflet. If you have any questions about this drug, please talk with your doctor, nurse, pharmacist, or other health care provider.
- This drug comes with an extra patient fact sheet called a Medication Guide. Read it with care. Read it again each time this drug is refilled. If you have any questions about this drug, please talk with the doctor, pharmacist, or other health care provider.
- If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.
© 2022 UpToDate, Inc. and its affiliates and/or licensors. All rights reserved.