This article describes possible side effects (also known as adverse effects) of metformin oral tablets. You’ll also find information on cost savings and coupon options for metformin.
Metformin immediate-release (IR) oral tablets* are a generic medication and don’t come in a brand-name version. Metformin extended-release (ER) oral tablets* are a generic medication of the brand names Fortamet and Glumetza. Metformin also comes as an oral suspension (a type of liquid mixture), but this form isn’t described in this article. To learn more about the oral suspension form, talk with your doctor.
You can explore this overview article to learn more about metformin oral tablets, including the drug’s uses, dosage, ways to save on cost, and more.
* With the IR form, the drug starts working as soon as you swallow the tablet. With the ER form, the drug works over time after you swallow the tablet.
Boxed warning: Risk of lactic acidosis
Metformin has a boxed warning for the risk of lactic acidosis. Boxed warnings are serious warnings from the Food and Drug Administration (FDA).
For details, see the “Side effects of metformin in detail” section below.
More common side effects of metformin
Metformin oral tablets may cause mild or serious side effects. Below are some of the more common side effects of this medication.
Commonly reported side effects in studies of metformin immediate-release oral tablets and metformin extended-release oral tablets include:
- headache
- pain in the abdomen
- indigestion (upset stomach)
- weakness
- gas
- vomiting
- diarrhea
- nausea*
* To learn more about this side effect, see the “Side effects of metformin in detail” section below.
Mild side effects of metformin
Metformin oral tablets may cause certain mild side effects. Usually, mild side effects are temporary and can be easily managed. Tell your doctor or pharmacist if you have side effects that don’t go away or become bothersome.
Mild side effects that occurred in studies of metformin immediate-release (IR) oral tablets and metformin extended-release (ER) oral tablets include:
* To learn more about this side effect, see the “Side effects of metformin in detail” section below.
† An allergic reaction is possible with metformin oral tablets. But it’s unclear whether it occurred in the drug’s studies of metformin IR oral tablets and metformin ER oral tablets.
Metformin may cause more mild side effects than those listed above. For details, see the prescribing information for metformin IR oral tablets and metformin ER oral tablets.
Serious side effects of metformin
Metformin oral tablets may cause certain serious side effects. If you have any serious side effects from metformin oral tablets, call your doctor right away. But if you think you’re having a medical emergency or your side effects feel life threatening, take immediate action. Call 911, or a local emergency number, or go to the nearest emergency room.
After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Visit MedWatch’s website if you’d like to notify the FDA about a side effect you’ve had with metformin oral tablets.
Serious side effects that occurred in studies of metformin immediate-release (IR) oral tablets and metformin extended-release (ER) oral tablets include:
* Metformin IR oral tablets and metformin ER oral tablets have a boxed warning for this side effect. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects of metformin in detail” section below.
† An allergic reaction is possible with metformin oral tablets. But it’s unclear whether it occurred in the drug’s studies. To learn more about this side effect, see the “Side effects of metformin in detail” section below.
Common questions about side effects of metformin
Here are answers to some common questions about side effects of metformin oral tablets. If you have other questions, talk with your doctor or pharmacist.
How do the side effects of metformin in women compare with those seen in men?
Studies of metformin immediate-release oral tablets and metformin extended-release oral tablets didn’t show differences in side effects between males* and females.*
However, metformin may cause ovulation (release of an egg from an ovary) in females with infertility (inability to become pregnant). For more information, talk with your doctor.
If you could become pregnant, talk with your doctor about birth control while you take metformin.
* Sex and gender exist on spectrums. In this article, we use the terms “male” and “female” to refer to a person’s sex assigned at birth.
Does the 500-mg strength of metformin cause different side effects than 1,000 mg?
No, the 500-milligram (mg) strength of metformin doesn’t cause different side effects than the 1,000-mg strength. But the side effects of the lower metformin dose* might be milder.
For example, the 500-mg strength of metformin is less likely to cause severe gas, nausea, and diarrhea than a 1,000-mg strength. That’s why your doctor will typically start your treatment with a 500-mg dose.
After your body gets used to the drug, your doctor will increase your dose until it has the desired effect. They’ll prescribe the lowest dose that manages your blood sugar.
If you have questions about what side effects to expect with your metformin dosage, talk with your doctor.
* To learn about the strengths and dosages of metformin, see this article.
Will I experience different side effects if I take metformin ER vs. metformin?
You might experience different side effects if you take metformin extended-release (ER) tablets versus metformin immediate-release (IR) tablets.
With the IR form, the drug starts working as soon as you swallow the tablet. With the ER form, the drug works over time after you swallow the tablet. Since the ER form of metformin is released into your body more slowly, it may cause fewer side effects. Or the side effects may be milder.
If you experience bothersome side effects from metformin IR tablets, you can ask your doctor about the ER form. They’ll help determine whether metformin ER is right for you. You can also read this article to learn about what to expect when you start metformin treatment.
Can metformin cause long-term side effects?
It’s possible for metformin to cause long-term side effects. Long-term side effects could be side effects that start while you take metformin or after you stop taking it.
Most side effects go away when you stop taking metformin. But there are some side effects that may occur during metformin treatment that have long-term consequences. This includes low vitamin B12 levels.
Even if you stop metformin, your B12 level may take a while to get back to its usual level. Your doctor may also suggest a supplement or injection of B12 to increase your levels. Fatigue (low energy) is a symptom of low B12 levels. If you experience this after you stop taking metformin, be sure to talk with your doctor.
If your child takes metformin and has nausea and vomiting that lead to weight loss, this could affect their growth. So even though nausea and vomiting aren’t long-term side effects of the drug, they can still be serious and cause long-term consequences.
If you have questions about long-term side effects with metformin, talk with your doctor.
Coupon for metformin
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Side effects of metformin in detail
Below you’ll find details on some of the side effects of metformin oral tablets.
Risk of lactic acidosis
Metformin has a boxed warning for the risk of lactic acidosis. Boxed warnings are serious warnings from the Food and Drug Administration (FDA). With lactic acidosis, you have a buildup of too much lactic acid in your blood. This can lead to hypothermia, low blood pressure, low heart rate, and in very rare cases, even death. Lactic acidosis was a rare side effect in studies of metformin immediate-release (IR) oral tablets and metformin extended-release (ER) oral tablets.
Symptoms of lactic acidosis to watch for include:
- slow or changed heart rate
- dizziness
- lightheadedness
- cold feeling in your arms and legs
- worsening problems with nausea, vomiting, or diarrhea
- excess sleepiness
- trouble breathing
- muscle pain
- weakness
- fatigue (low energy)
You may have an increased risk of lactic acidosis if you:
- have kidney, liver, or heart problems
- are age 80 or older
- drink alcohol excessively
- have had recent surgery
- are dehydrated
- have a severe infection
- have had a stroke
- recently used contrast dyes for imaging tests
Ways to manage
Lactic acidosis is a medical emergency. If you have symptoms of lactic acidosis, immediately tell your doctor. You’ll likely need to go to the hospital right away to receive treatment for lactic acidosis.
If you have lactic acidosis, your doctor will likely recommend that you stop taking metformin. Talk with your doctor about what to do if you think you have an increased risk of lactic acidosis.
To help make sure that you aren’t developing symptoms of lactic acidosis, it may be helpful to keep track of your symptoms in a notebook or app. This way, you’re more likely to notice a new symptom.
There are also ways to avoid lactic acidosis. If you have to use contrast dye or have surgery, your doctor may temporarily stop your metformin treatment. They may also avoid prescribing drugs that interact with metformin and increase your risk of this side effect. These drugs include cimetidine, dolutegravir, and acetazolamide.
Weight loss
Weight loss can occur with metformin treatment. This was a common side effect in studies of metformin IR oral tablets and metformin ER oral tablets. But the amount of weight loss was small. The most weight loss that was reported was about 3 pounds. People who took metformin along with other diabetes medications lost more weight.
Other side effects of metformin may cause you to eat less, which may lead to weight loss. These side effects include:
- nausea
- indigestion (upset stomach)
- heartburn
- gas
- vomiting
- diarrhea
Ways to manage
Talk with your doctor if you notice a sudden or significant change in your weight. They may decrease your metformin dose.* If you’re interested in managing your weight, they can help you figure out the best way to do so.
* To learn about the dosages of metformin, see this article.
Nausea
Nausea was a common side effect in studies of metformin IR oral tablets and metformin ER oral tablets. Nausea can make it difficult to eat or drink, and it can also interrupt daily activities. Nausea from metformin can be mild and usually eases after a few weeks. It’s more likely with higher metformin doses.*
If you experience sudden, severe nausea, this could be a sign of lactic acidosis.† This is a medical emergency that requires treatment in a hospital.
Ways to manage
Your doctor will typically prescribe a low dose of metformin when you start treatment. This way, your body has a chance to get used to the drug. This may help reduce the risk of side effects.
Other ways to avoid or reduce nausea with metformin include:
- taking your metformin dose with a meal
- avoiding crushing metformin tablets before taking them
- avoiding alcohol, if applicable
- eating a bland diet
- taking an over-the-counter nausea treatment
Talk with your doctor about other ways to reduce nausea while you take metformin. If your nausea is severe or doesn’t go away, talk with your doctor. You can ask your doctor about metformin ER tablets. This form of metformin releases the drug slowly, which may help reduce the risk and severity of side effects.
* To learn about the dosages of metformin, see this article.
† Metformin IR oral tablets and ER oral tablets have a boxed warning for this side effect. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). To learn more, see “Risk of lactic acidosis” above.
Allergic reaction
For some people, metformin can cause an allergic reaction. But it’s not clear whether this side effect occurred in studies of metformin IR oral tablets and metformin ER oral tablets.
Symptoms can be mild or serious, and they may include:
- itchiness
- skin rash
- swelling under the skin, usually affecting eyelids, lips, hands, or feet
- swelling of the mouth, tongue, or throat, which can make it hard to breathe
- flushing (temporary warmth, redness, or deepening of skin color)
Ways to manage
For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.
For severe allergic reaction symptoms, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to metformin oral tablets, your doctor may recommend taking a different medication instead.
Warnings for metformin
Below are some factors you may want to discuss with your doctor before taking metformin oral tablets.
Boxed warning: Risk of lactic acidosis
Metformin has a boxed warning for the risk of lactic acidosis. Boxed warnings are serious warnings from the Food and Drug Administration (FDA).
For details, see the “Side effects of metformin in detail” section above.
Other warnings
Before taking metformin oral tablets, tell your doctor about your health and medications you take. Things to consider include those listed below.
It may not be safe for you to take metformin oral tablets if you have specific health conditions. These are sometimes called drug-condition interactions. Other things may also affect whether metformin oral tablets are a safe treatment option for you.
Heart disease. Metformin may cause changes in heart rate. If you already have heart problems, metformin could make them worse. If you have heart failure, you may also have an increased risk of lactic acidosis.* Talk with your doctor about the risks and benefits of metformin if you have heart disease.
Surgery. If you have surgery planned, be sure to tell your doctor. They may temporarily pause your metformin treatment. Surgery typically requires fasting, which may impact your kidney function. This may also increase your risk of side effects with metformin. Talk with your doctor about your kidney function after surgery and when you can restart metformin treatment.
Imaging. If you plan to get an X-ray or MRI, your doctor may pause your metformin treatment. Some contrast dyes used in scans can increase your risk of lactic acidosis.* Talk with your doctor about how long to pause your metformin treatment.
Liver problems. Your liver helps remove metformin from your body. So, if you have low liver function, you may have an increased risk of having high levels of metformin in your blood. This increases your risk of side effects, especially lactic acidosis.* Talk with your doctor about monitoring your liver function while you take metformin.
Kidney problems. Metformin is removed from your body using your kidneys. If your kidney function is low, you may have an increased risk of side effects from metformin. Talk with your doctor about having kidney function tests. They may lower your metformin dose† or monitor your kidney function more often.
Older adults. Adults ages 80 years and older have an increased risk of decreased kidney function. If you are age 80 years or older, talk with your doctor about having kidney function tests. You may have a higher risk of side effects from metformin if you have kidney problems.
Allergic reaction. If you’ve had an allergic reaction to metformin or any of its ingredients, your doctor will likely not prescribe this medication. Ask them about other treatment options that may be better for you.
* Metformin immediate-release (IR) oral tablets and metformin extended-release (ER) oral tablets have a boxed warning for this side effect. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects of metformin in detail” section above.
† To learn about the dosages of metformin, see this article.
Metformin and pregnancy
It’s not known whether it’s safe to take metformin oral tablets during pregnancy. Studies of metformin IR oral tablets and metformin ER oral tablets are limited. It’s unknown whether the benefits of metformin outweigh the risks during pregnancy.
Metformin may cause ovulation (release of an egg from an ovary) in females with infertility (inability to become pregnant). For more information, talk with your doctor.
Talk with your doctor about the risks and benefits of taking metformin during pregnancy.
Note: Metformin is not approved to treat infertility.
Metformin and breastfeeding
It’s unknown whether metformin oral tablets are safe to take while breastfeeding. Studies of metformin IR oral tablets and metformin ER oral tablets taken while breastfeeding were limited. More studies are needed to determine whether metformin is safe to take while breastfeeding.
Talk with your doctor about the risks and benefits of taking metformin tablets while breastfeeding.
Metformin and alcohol
Metformin oral tablets are known to interact with alcohol.
Alcohol lowers your blood sugar temporarily. Metformin also lowers blood sugar. So taking both together could increase your risk of low blood sugar further.
Alcohol use also increases your risk of lactic acidosis,* a serious side effect of metformin.
If you drink alcohol, talk with your doctor about whether it’s safe to consume it during your treatment with metformin.
* Metformin IR oral tablets and metformin ER oral tablets have a boxed warning for this side effect. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects of metformin in detail” section above.
What to ask your doctor
This article describes common and serious side effects of metformin oral tablets. If your doctor prescribes this medication, they can discuss possible side effects with you. Let your doctor know if you have concerns or questions about treatment with this medication.
Here’s a list of some possible questions you may want to ask your doctor:
- Can metformin worsen memory loss?
- How long will it take for the nausea and diarrhea from metformin to go away?
- Can metformin cause weight gain?
- If I have polycystic ovary syndrome (PCOS), will my metformin side effects be worse?
- If I have kidney damage, are other diabetes drugs safer for me than metformin?
Disclaimer: Optum Perks 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 another 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.
