Comparing Metformin ER Brands: Glucophage XR vs. Glumetza vs. Fortamet

Metformin is a popular medication for Type 2 diabetes. In fact, the American Diabetes Association (ADA) recommends it as a first-choice treatment option. 

Metformin is available in two forms: immediate-release (IR) and extended-release (ER). The ER forms are often referred to by one of their three brand names: Glucophage XR, Glumetza, and Fortamet. Each brand also has its own generic version. Here, we’ll walk through how the metformin ER brands compare.

Note: Brand-name Glucophage XR is no longer available on the U.S. market. But to avoid confusion, we’ll use brand names throughout this article. That way, you know exactly which metformin ER we’re talking about.

How do Glucophage XR, Glumetza, and Fortamet work?

Metformin, the active ingredient in all three brands of metformin ER, helps to lower your blood sugar (glucose) levels by:

• Making it easier for your cells to absorb and use glucose

• Lowering the absorption of glucose in your intestines, so less enters your bloodstream

• Decreasing the production of glucose in your liver 

Is Glucophage XR, Glumetza, or Fortamet more effective for diabetes?

These metformin brands are similarly effective at treating Type 2 diabetes. In fact, the ADA doesn’t have a preference for which one you should use.  

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Metformin ER does have some advantages over metformin IR, though. Higher doses of metformin IR need to be split up throughout the day, while metformin ER can be taken once a day, even at high doses. This can help make it easier to remember to take your medication consistently. 

Also, metformin ER may cause fewer side effects than metformin IR in some people, which means you might be able to better tolerate a higher dose if needed.

How are Glucophage XR, Glumetza, and Fortamet dosed and taken?

All three brands of metformin ER are taken by mouth, generally once a day with your evening meal. Taking them with food can help prevent an upset stomach, which is a common side effect. Do not crush, cut, or chew these medications, as it will change how your body absorbs them and could lead to more side effects.

Metformin ER dosing

Brand-name metformin ER medications (and their corresponding generics) are available in the following doses:

• Glucophage XR: 500 mg and 750 mg

• Glumetza: 500 mg and 1,000 mg

• Fortamet: 500 mg (generic version only) and 1,000 mg (brand name and generic)

Dosing for metformin will depend on how you respond to it. Because metformin can cause stomach problems like diarrhea, nausea, or gas, most people start off with lower doses of 500 mg a day. After several weeks, your healthcare provider may increase your daily dose by 500 mg at a time to a maximum of 2,000 mg a day. People with kidney problems may be prescribed lower doses to help avoid complications.

Which medications interact with metformin ER?

Metformin can be taken with most medications.

Some medications metformin may interact with are:

• Insulins

• Sulfonylureas like glipizide

• Corticosteroids like prednisone

• Thiazide diuretics like hydrochlorothiazide

• Antipsychotic medications like quetiapine (Seroquel)

• Topiramate (Topamax)

• Cimetidine (Tagamet HB)

You can manage most interactions with dose changes or closer monitoring.

While you’re taking metformin, you should also avoid alcohol, which may increase the risk of lactic acidosis (more on this below).

This is not an all-inclusive list of things that can interact with metformin. Always talk to your healthcare provider and pharmacist about the medications and supplements you are taking before starting a new medication. Keeping an up-to-date medication list can be a helpful tool for managing interactions.

What are the most common side effects of Glucophage XR, Glumetza, and Fortamet?

Brands of metformin ER haven’t been directly compared in large clinical trials. So we don’t know how they match up against each other in terms of side effects. However, here are some of metformin’s most notable side effects:

• Upset stomach: Many people who take metformin have diarrhea, upset stomach, and gas. Metformin ER is believed to be less likely to cause these side effects than metformin IR. But a large review of multiple studies wasn’t able to say that for sure. What is known for certain is that stomach-related problems are the most common side effects of all forms of metformin.

• Vitamin B12 deficiency: Taking metformin can cause low vitamin B12 levels, which in turn can cause anemia. Signs of anemia include low energy, muscle weakness, low appetite, and tingling sensations in your hands and feet. This can worsen nerve pain for some people.

While you’re taking metformin, your healthcare provider may ask you to get certain blood tests to monitor your kidney function, vitamin B12 levels, and blood glucose levels. These tests help your provider to see how well the medication is working and if you’re having any serious side effects.

Should I be concerned about lactic acidosis?

Lactic acidosis, a serious condition resulting from too much lactic acid in your blood, is possible while taking metformin. However, it's extremely rare. Poor kidney function is thought to make it more likely. Other risk factors for lactic acidosis include alcohol use, history of liver disease, and current severe illnesses like sepsis.

Lactic acid is a normal waste product that is processed through your kidneys and then leaves your body through your urine. However, metformin can cause lactic acid to build up. Too much lactic acid in the blood can lead to confusion, a fast heartbeat, and rapid breathing. If not treated, lactic acidosis can become life-threatening.

Who shouldn’t take metformin ER?

If you have poorly functioning kidneys (like in stage 4 or 5 chronic kidney disease), metformin ER may not be the safest diabetes treatment option for you. As mentioned above, kidney problems can raise the risk of lactic acidosis.

You should also discuss metformin ER with your healthcare provider if you’re pregnant or would like to become pregnant. While metformin is safe to take during pregnancy, insulin is typically preferred.

How to save on Glucophage XR, Glumetza, and Fortamet

Glucophage XR, Glumetza, and Fortamet are available as lower-cost generics. GoodRx can help you save over 70% off the average retail price of the generic versions.

Generic Glucophage XR's price at certain pharmacies is as low as $17.46 with a free GoodRx discount. Generic Glumetza's price at certain pharmacies is as low as $59.41 with a free GoodRx discount. Generic Fortamet's price at certain pharmacies is as low as $34.10 with a free GoodRx discount.

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Written by:

Timothy Aungst, PharmD

Timothy Aungst, PharmD, has worked in pharmacy practice for the past decade with different roles and responsibilities. He has served as an associate professor of pharmacy practice for almost a decade, a clinical pharmacist in outpatient cardiology management, and now in home healthcare.

Edited by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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