Metformin, Metformin ER

Introduction

Written by Helen Marshall BPharm MRPharmS
Medically reviewed by Rosanna Sutherby, PharmD
Updated on July 27, 2023

Metformin (met FOR min) is a generic medication prescribed to help manage blood sugar levels in adults and some children with type 2 diabetes. Metformin belongs to a group of drugs called biguanides.

This article doesn’t provide coupons for all forms of metformin. To find coupons for metformin extended-release oral tablet, see this article.

Boxed warning: Risk of lactic acidosis

Metformin has a boxed warning for the risk of lactic acidosis. Boxed warnings are the most serious warnings from the Food and Drug Administration (FDA).

For details, see the “Interactions and warnings for metformin” section.

Side effects of metformin

Metformin may cause mild or serious side effects. More common mild side effects of metformin and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about metformin’s side effects, see this article or ask your doctor or pharmacist. You can also refer to the prescribing information for metformin listed in the “Resources” section.

Mild side effects

More common mild side effects reported with some forms of metformin are listed below. These side
effects may differ based on the form of metformin you take.

This article doesn’t include all possible mild side effects of the drug. To learn more about metformin’s side effects based on the form, refer to the prescribing information for metformin listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Mild side effects of metformin oral tablet, extended-release oral tablet, and oral solution include:

• diarrhea
• nausea and vomiting
• gas
• feeling weak
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for metformin” section.

Serious side effects

Serious side effects of metformin are listed below.

This article doesn’t include all possible serious side effects of the drug. To learn more about metformin’s side effects, refer to the prescribing information for metformin listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, metformin’s serious side effects include:

• low blood sugar level
• low vitamin B12 level
• boxed warning: risk of lactic acidosis*
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for metformin” section.

Common questions about metformin

Below you’ll find answers to a few commonly asked questions about metformin.

Can metformin be used for weight loss?

Metformin can cause weight loss in some people. For people with type 2 diabetes who are overweight, this side effect can be beneficial. But doctors don’t typically prescribe metformin for weight loss in people who don’t have diabetes or high blood sugar levels.

Certain other medications originally designed to treat types 2 diabetes have recently been approved for aiding weight loss. Examples include semaglutide (Wegovy) and liraglutide (Saxenda).

If you’re interested in taking medication to help with weight loss, talk with your doctor.

What are the signs that metformin is working?

The best way to know if metformin is working is by checking your blood sugar levels. Metformin is prescribed to help lower your blood sugar levels. If your blood sugar levels remain high, metformin may not be working for you.

Your doctor may recommend checking your blood sugar yourself at home using a blood glucose meter. Your doctor will also likely order A1C blood tests every few months. This test measures your average blood sugar levels over the past 3 months.

If you have questions about how to tell if metformin is working for you, talk with your doctor.

How does metformin work? And how long does it take to start working?

Metformin works in three ways to help lower your blood sugar levels. It reduces the amount of sugar that gets absorbed into your blood after you eat or drink. It also reduces the amount of sugar your liver makes. As well, it helps cells in your body remove sugar from your blood.

Metformin usually starts working within 48 hours, but it may take up to a week before your blood sugar levels start to improve.

If you’d like to know more about how metformin works, talk with your doctor or pharmacist.

Uses of metformin

The Food and Drug Administration (FDA) approves prescription drugs such as metformin for certain conditions. Approved uses for metformin are described below.

Use for type 2 diabetes

Doctors may prescribe metformin to help manage blood sugar levels in people with type 2 diabetes. Metformin oral tablet and oral solution are prescribed for this purpose in adults and children ages 10 years and older. Metformin extended-release* oral tablet is prescribed for this purpose in adults. It’s usually a long-term treatment.

With type 2 diabetes, cells in your body become resistant to the effects of insulin. Insulin is a hormone that usually helps your cells remove sugar from your blood after eating or drinking. When cells become resistant to insulin, your blood sugar levels can get too high.

Over time, high blood sugar levels can damage tissues in your body and lead to complications of diabetes. These include nerve damage, kidney problems, problems with eyesight, and heart disease.

Metformin helps lower your blood sugar levels. It’s prescribed along with a nutritious diet and regular physical activity such as exercising to help manage your blood sugar levels. This can help prevent complications of diabetes.

* Extended-release tablets release the medication slowly over a period of time, rather than all at once.

Interactions and warnings for metformin

Below, you’ll find information about metformin’s possible interactions and warnings.

Interactions of metformin

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol* or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take metformin, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for metformin” section below.

* You should avoid drinking large amounts of alcohol while taking metformin, as this can raise your risk of lactic acidosis. Metformin has a boxed warning for this side effect. To learn more, see the “Warnings for metformin” section below.

Warnings for metformin

Some people should not take metformin, and others should take it cautiously.

Boxed warning: Risk of lactic acidosis

Metformin has a boxed warning about the risk of lactic acidosis. Boxed warnings are the most serious warnings from the Food and Drug Administration (FDA).

With lactic acidosis, you have a buildup of lactic acid in your blood. This is a medical emergency that can be fatal.

This side effect is rare. It wasn’t reported in studies of metformin, but it has occurred since the drug was approved.

Symptoms of lactic acidosis may include:

• unusual sleepiness
• feeling weak and generally unwell
• muscle aches
• abdominal pain
• trouble breathing or breathing faster than usual
• dizziness
• slow heart rate

If you experience symptoms of lactic acidosis, stop taking metformin and call your doctor right away. But if your symptoms feel life threatening, call 911 or your local emergency number. This condition is life threatening and needs to be treated in a hospital.

To learn more, talk with your doctor or pharmacist.

Other warnings

Metformin could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether metformin is a safe option for you.

Ask your doctor about specific warnings for metformin, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Metformin can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to metformin or any of its ingredients, your doctor will likely not prescribe metformin. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to metformin, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of metformin

You should not take more metformin than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much metformin, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and metformin

Information about metformin and pregnancy and breastfeeding is described below.

Metformin and pregnancy

There may be risks of taking metformin during pregnancy. But there are also risks with having
unmanaged type 2 diabetes while pregnant. (Metformin is prescribed to help manage type 2 diabetes.)

If you’re planning a pregnancy or can become pregnant, talk with your doctor about type 2 diabetes treatment options during pregnancy. Together, you can discuss the risks and benefits of your treatment options and decide whether you should take metformin during pregnancy.

Metformin and breastfeeding

In general, metformin is considered safe to take while breastfeeding. That said, ask your doctor about whether they feel it’s safe for you.

What to ask your doctor

Let your doctor know if you have questions about metformin or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• How effective is metformin?
• If metformin doesn’t work for me, will I need to take other medications?
• Does metformin have any long-term side effects?
• What other treatment options are available for me?

Resources

• Metformin. (2022). https://www.ncbi.nlm.nih.gov/books/NBK501020/
• Metformin hydrochloride oral solution. (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/73691c6c-8841-4c5d-b4a5-c3ed3b5effa1/spl-doc
• Metformin hydrochloride tablet, for oral use. (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/a2385bcd-0943-4411-8658-c22b50360385/spl-doc
• Metformin hydrochloride tablet, extended release. (2019). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/4833deea-a19d-63b1-e054-00144ff8d46c/spl-doc?hl=metformin%20hydrochloride%20extended%20release
• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Yerevanian A, et al. (2019). Metformin: Mechanisms in human obesity and weight loss. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6520185/

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.