Metformin vs. Metformin ER: Which One Is Right for Me?

Metformin has been a go-to medication for people with Type 2 diabetes for decades. If you’ve been diagnosed with prediabetes or Type 2 diabetes, you’ve probably heard of metformin. This medication isn’t known only for its benefits on blood sugar — it’s also recommended for its low cost and other health benefits.

In this article, we’ll talk more about metformin: How regular, immediate-release (IR) metformin is different from extended-release (ER) metformin, what the typical metformin dosage is, and what its side effects are.

How does metformin work?

Metformin improves blood sugar levels by lowering the amount of glucose (sugar) that we absorb from our diet. It also helps stop the production of new glucose and improves insulin sensitivity. Insulin is a hormone that signals your body to use glucose for energy. In turn, this lowers the amount of sugar in your blood. 

One of the unique things about metformin, compared to other diabetes medications, is that it does not usually cause low blood sugar (hypoglycemia).

What is the difference between metformin IR and metformin ER?

Metformin IR and metformin ER are the same medication, except that metformin ER is the extended-release version of immediate-release (IR), or “regular” metformin. This means that metformin ER is slowly absorbed into the bloodstream compared to metformin IR. 

Since metformin ER dosage form works for a longer period of time, it can be taken less frequently.  

What are the generic and brand versions of metformin?

Metformin IR is the generic version of brand-name Glucophage. However, Glucophage is no-longer available in the U.S. 

There are 3 generic versions of metformin ER tablets. Each was developed from a different brand-name medication: 

• Glucophage XR (brand no longer available)

• Glumetza

• Fortamet

These ER versions differ in terms of how they are made, which you can read about in a previous GoodRx Health article. Also note that a liquid version of metformin ER (Riomet ER) is no longer available in the U.S. 

Metformin IR, ER, and their respective brand-name versions are available in the following dosages: 

• Metformin IR tablets: 500 mg, 850 mg, and 1,000 mg

• Metformin IR oral liquid (Riomet): 500 mg/5 mL

• Metformin ER: 500 mg and 750 mg

• Metformin ER (Glumetza): 500 mg and 1,000 mg

• Metformin ER (Fortamet): 500 mg and 1,000 mg

Is metformin IR or metformin ER better for diabetes?

One version isn’t better than the other. Both are approved to treat Type 2 diabetes alongside a healthy diet and exercise routine. 

Metformin products have been shown to lower the risk of diabetes complications for people who use them long-term. For example, metformin doesn’t typically cause weight gain. In fact, it can cause healthy weight loss, and it can lower the risk of cardiovascular events (e.g. heart attack) in people with Type 2 diabetes.

Metformin may also be recommended for prediabetes in some people. These can include:

• People who have BMI greater than 35

• People with an A1C higher than 6%

• People younger than 60

• Women who have experienced gestational diabetes (diabetes during pregnancy) in the past

You can read more about metformin and prediabetes in this GoodRx Health article.

So, both metformin dosage forms are go-to options to consider. Adults, however, might prefer metformin ER over the IR version because they can take fewer doses per day with fewer side effects. But only metformin IR is FDA-approved in children who are at least 10 years old. Metformin ER can only be used by adults ages 18 and older. 

How are metformin IR and metformin ER doses taken?

Metformin IR and ER should be taken by mouth with food. Taking it with food may help prevent stomach aches. For metformin ER, remember to not split, crush, or chew the tablets — make sure to swallow them whole. 

Metformin dosage

The dosage for Metformin IR and ER tend to be adjusted over time based on how you respond to the medication. Some of the most common side effects of metformin products are upset stomach and diarrhea. For that reason, your healthcare provider may start you at a low dose and then raise it slowly over time.

Keep in mind that your metformin IR or ER dosages may also vary depending on your kidney function and medication interactions.

Metformin IR dosage 

When you first start taking metformin IR, your initial dose is usually one 500 mg tablet by mouth, 2 times daily with food. You could also take one 850 mg tablet once daily. 

It’s possible that you will take this dose over time. But as mentioned, depending on your blood sugar goals and how you respond to the medication, your healthcare provider may choose to slowly raise your metformin dose over a few weeks. It may be increased by 500 mg to 850 mg every 1 to 2 weeks, up to a maximum daily dose of 2,550 mg. High daily doses are usually divided into two or three smaller doses throughout the day.

Metformin ER dosage

Generally, metformin ER dosage starts at 500 mg once daily with food. Similar to the IR version, your healthcare provider may choose to increase your dose by 500 mg every 1 to 2 weeks up to a maximum of 2,000 mg once daily. 

What medications interact with metformin IR and metformin ER?

You can typically take metformin IR or ER with most of your other prescriptions. Metformin IR or ER doesn’t have a lot of interactions. 

But in general, use caution with alcohol, which can raise your lactic acidosis risk. Lactic acidosis occurs when there is a dangerous amount of lactic acid in the body. This chemical is made when oxygen levels become low. Lactic acidosis is also more likely if you take medications that make your blood more acidic, such as acetazolamide (Diamox) for altitude sickness. 

Also, be careful with medications that block the kidneys from clearing out metformin from the body, like cimetidine (Tagamet HB) for acid reflux. Side effects are more likely if you have higher metformin levels.

These are some key interactions with metformin IR and ER, but it’s not a complete list. For more information on metformin interactions, talk to your pharmacist or healthcare provider about your up-to-date medication list.

What are the most common side effects of metformin IR and metformin ER?

Although metformin is relatively safe there are some side effects you should be aware of, such as:

• Diarrhea

• Constipation

• Nausea and vomiting

• Gas and bloating

• Heartburn

• Stomach upset

• Changes in taste

Long-term use of metformin IR or ER can also lead to lower levels of vitamin B12 in the body, which can contribute to anemia. Your provider will likely ask you to get blood tests every year to make sure this isn’t a problem.

Is lactic acidosis a concern?

Metformin IR or ER can cause lactic acidosis, but it’s very uncommon. 

But as discussed earlier, certain medication interactions, alcohol use, and kidney problems can make lactic acidosis a more likely event.  

Who shouldn’t take metformin?

While metformin IR is an effective go-to option for Type 2 diabetes and prediabetes, metformin isn’t for everyone. Avoid metformin IR or ER if any of the following apply to you.

• Severe allergic reaction: If you’ve had a severe allergic reaction to metformin or its ingredients in the past, metformin isn’t recommended. Symptoms of a severe allergic reaction may include breathing difficulties, severe itchiness, and swelling.

• Severe kidney problems: Poorly functioning kidneys can cause metformin to build up in your body. This can worsen your risk of lactic acidosis. 

• Diabetic ketoacidosis (DKA): DKA is a life-threatening complication of diabetes. It happens when your body breaks down fat too quickly and your liver turns the fat into ketones, which can make your blood acidic. It might also lead to having fruity breath, extreme thirst, and trouble staying alert. If you have DKA, metformin isn’t the best choice for you.

How to save on metformin IR and metformin ER

Metformin IR and metformin ER are both available as lower-cost generics. GoodRx can help you save over 87% off the average retail price of the generic versions of metformin IR and metformin ER. Generic metformin IR’s price at certain pharmacies is less than $6 with a free GoodRx discount. Generic metformin ER’s price at certain pharmacies is less than $8 with a free GoodRx discount.

Can I take metformin for a long time?

Yes, metformin IR or ER can typically be taken for a long time. While long-term metformin IR or ER use may cause low vitamin B-12, it is usually safe for long-term use.

But there might be times when your healthcare provider will stop it. For more information about long-term metformin use, talk with your pharmacist or healthcare provider.

Why trust our experts?

Written by:

Ross Phan, PharmD, BCACP, BCGP, BCPS

Ross Phan is a board-certified clinical pharmacist. She has roughly two decades of healthcare experience — with most of her experience being pharmacy related.

Edited by:

Samvida Patel, MNSP, INHC

Samvida Patel, MNSP, INHC, is a health editor at GoodRx. She is a nutritionist and integrative nutrition health coach with over 8 years of experience in health communications.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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