Key takeaways:
Metformin is available in two forms: immediate-release (IR) and extended-release (ER). Compared with metformin IR, the ER form is designed to release the medication at a slower rate.
Metformin IR is usually taken multiple times a day, while metformin ER is taken once daily. Metformin ER may also be less likely to cause gastrointestinal side effects.
Metformin IR and metformin ER are both available as lower-cost generics. GoodRx can help you save over 50% off the average retail price at certain pharmacies.
Save on related medications
Metformin has been a cornerstone treatment for Type 2 diabetes for decades. If you’ve been diagnosed with prediabetes or Type 2 diabetes, it’s likely one of the first medications you’ve heard about. In addition to helping lower blood glucose (blood sugar), metformin is widely recommended because it’s effective, affordable, and well-studied.
Metformin is available in two forms: immediate-release (IR) and extended-release (ER). Both work well, but they differ in how they’re taken and how people tolerate them. Here’s how metformin IR and metformin ER compare.
How does metformin work?
No matter which form you’re prescribed, metformin works a few different ways in the body to help lower blood sugar levels:
Reduces sugar production in the liver, which lowers fasting blood sugar levels
Improves insulin sensitivity, helping your body use insulin more effectively
Decreases absorption of sugar from the gut after meals
Unlike some diabetes medications, metformin doesn’t trigger insulin release. Because of this, it doesn’t usually cause low blood sugar (hypoglycemia) when taken on its own.
What is the difference between metformin IR and metformin ER?
Metformin IR and metformin ER contain the same active ingredient, but metformin ER is the long-acting version of immediate-release, or “regular” metformin. Metformin ER is designed to release the medication more slowly over time. Here are the key differences.
Metformin IR | Metformin ER | |
|---|---|---|
How it’s released | Fast, immediate release | Slow release over hours |
About 6 hours | About 12 hours | |
1-3 times daily | Once daily | |
Side effects | May be more likely | May be less likely |
What are the generic and brand versions of metformin?
Metformin IR and metformin ER are available only as generic medications. All of the original brand-name products have been discontinued. There are also several generic metformin ER products, which use different release mechanisms to deliver the medication over time.
Is metformin IR or metformin ER better for diabetes?
Neither version is considered better overall. Both metformin IR and metformin ER are FDA approved to treat Type 2 diabetes. The best fit for you can depend on your age, preferences, and tolerability.
When choosing between the two forms, some people may prefer metformin ER because it’s taken once daily and tends to cause fewer gastrointestinal side effects. However, metformin IR is the only form approved for children ages 10 and older, while all ER forms are approved for adults only.
How are metformin IR and metformin ER taken?
Metformin IR and metformin ER should be taken by mouth with food. Taking your doses with food may help reduce gastrointestinal side effects, such as nausea and diarrhea. For metformin ER, don’t split, crush, or chew the tablets — make sure to swallow them whole.
No matter which form you take, metformin is usually started at a low dose and increased gradually to help your body adjust. Your prescriber will recommend a dosage schedule that best fits your treatment goals, tolerance, and daily routine. Here’s how their recommended dosages compare.
Metformin IR dosage | Metformin ER dosage | |
|---|---|---|
Starting dosage (lowest dose) | 500 mg twice daily or 850 mg once daily with food | 500 mg once daily with evening meal |
Maximum dosage | 2,550 mg for adults and 2,000 mg for children (taken in divided doses) | 2,000 mg once daily |
What medications interact with metformin IR and metformin ER?
Since they contain the same active ingredient, metformin IR and metformin ER can interact with the same medications. Most interactions require closer monitoring or dosage adjustments, rather than avoiding the combination altogether.
Medications and substances that may interact with metformin IR and metformin ER include:
Iodinated contrast dye
Other diabetes medications, especially insulin and sulfonylureas
Cimetidine (Tagamet HB)
Carbonic anhydrase inhibitors, such as acetazolamide and topiramate (Topamax)
Medications that raise blood sugar levels, such as corticosteroids
Always tell your healthcare team about all medications and supplements you take. They can help determine whether metformin is safe to take with your other treatments.
What are the most common side effects of metformin IR and metformin ER?
Metformin IR and metformin ER can cause similar side effects, though they may be less frequent or milder with ER forms. Most side effects affect the digestive system, and they’re more noticeable when starting metformin or increasing the dose.
Common metformin side effects include:
Diarrhea
Nausea
Stomach upset or cramping
Gas or bloating
Heartburn
Metallic taste in the mouth
Long-term use of metformin IR or metformin ER can also lead to lower levels of vitamin B12 in the body. Your prescriber will likely ask you to get blood tests every year to make sure this isn’t a problem. If your levels get too low, they may suggest taking a vitamin B12 supplement.
While uncommon, metformin can cause a life-threatening condition called lactic acidosis, which is a buildup of lactic acid in the body. Certain factors can increase the risk of lactic acidosis while taking metformin, including:
Severely reduced kidney function
Liver disease
Heavy or frequent alcohol use
Heart failure
Older age
Taking certain medications that interact with metformin
Who shouldn’t take metformin IR or metformin ER?
Metformin is safe and effective for many people, but it isn’t appropriate for everyone. You may be advised not to take metformin if you:
Have severely reduced kidney function
Are allergic to metformin or any of its inactive ingredients
Have liver disease
Have too much acid in your blood
Drink large amounts of alcohol regularly
Your healthcare team will review your medical history to ensure that metformin is a safe option 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 50% off the average retail price. With GoodRx, the price of generic metformin IR is as low as $9.00 and the price of generic metformin ER is as low as $9.00 at certain pharmacies.
Frequently asked questions
Yes, metformin is typically meant to be taken long term. Your prescriber will likely recommend continuing it as long as it’s working for you and the side effects are manageable. With regular monitoring, such as tests for your kidney function and vitamin B12 levels, many people take metformin safely for years.
In addition to treating diabetes, metformin may offer other health benefits. Some people may lose weight while taking it. Metformin can also improve insulin sensitivity, which is why it’s commonly used for health conditions such as prediabetes and polycystic ovary syndrome (PCOS).
Some research suggests that metformin may lower the risk of certain cardiovascular events and cancers, but these potential benefits are still being studied.
Yes, it’s possible to switch between metformin IR and metformin ER. Some people switch to improve tolerability or simplify their dosage schedule. Metformin ER is commonly used if the IR form causes bothersome stomach side effects or if a once-daily dosage is preferred. A healthcare professional can help adjust the dose and timing when you’re making a switch.
No, you’ll typically take metformin IR or metformin ER — but not both at the same time. Taking both forms together isn’t recommended and usually doesn’t provide any additional benefit.
Yes, metformin is typically meant to be taken long term. Your prescriber will likely recommend continuing it as long as it’s working for you and the side effects are manageable. With regular monitoring, such as tests for your kidney function and vitamin B12 levels, many people take metformin safely for years.
In addition to treating diabetes, metformin may offer other health benefits. Some people may lose weight while taking it. Metformin can also improve insulin sensitivity, which is why it’s commonly used for health conditions such as prediabetes and polycystic ovary syndrome (PCOS).
Some research suggests that metformin may lower the risk of certain cardiovascular events and cancers, but these potential benefits are still being studied.
Yes, it’s possible to switch between metformin IR and metformin ER. Some people switch to improve tolerability or simplify their dosage schedule. Metformin ER is commonly used if the IR form causes bothersome stomach side effects or if a once-daily dosage is preferred. A healthcare professional can help adjust the dose and timing when you’re making a switch.
No, you’ll typically take metformin IR or metformin ER — but not both at the same time. Taking both forms together isn’t recommended and usually doesn’t provide any additional benefit.
The bottom line
Metformin comes in two forms: immediate-release (IR) and extended-release (ER). They both work the same way to treat Type 2 diabetes. But metformin ER is designed to release more slowly over time and may be less likely to cause gastrointestinal side effects.
The best option for you can depend on your preferences, tolerability, and daily routine. Your prescriber can help determine whether metformin IR or metformin ER is a better fit.
Why trust our experts?
References
American Diabetes Association. (2022). Standards of Medical Care in Diabetes — 2022 Abridged for Primary Care Providers. Clinical Diabetes.
Bryant Ranch Prepack. (2020). Metformin hydrochloride- metformin hydrochloride tablet, extended release [package insert].
Bu, Y. (2022). Protective effects of metformin in various cardiovascular diseases: Clinical evidence and AMPK-dependent mechanisms. Journal of Cellular and Molecular Medicine.
DeFronzo, R., et al. (2016). Metformin-associated lactic acidosis: Current perspectives on causes and risk. Metabolism.
Han, Y., et al. (2019). Effect of metformin on all-cause and cardiovascular mortality in patients with coronary artery diseases: A systematic review and an updated meta-analysis. Cardiovascular Diabetology.
Kim, S. (2023). Metformin-associated lactic acidosis (MALA): Is it an underestimated entity? A retrospective, single-center case series. Hemodialysis International.
MedlinePlus. (2024). Lactic acidosis.
MedlinePlus. (2024). Metformin.
MedlinePlus. (2025). Diabetic ketoacidosis.
Nasri, H., et al. (2014). Metformin: Current knowledge. Journal of Research in Medical Sciences.
National Kidney Foundation. (2024). Metabolic acidosis.
Pala, L., et al. (2014). The “slower” the better. Journal of Endocrinological Investigation.
Time Cap Laboratories. (2025). Metformin HCL tablet, film coated [package insert].
U.S. Food and Drug Administration. (n.d.). Drugs@FDA: FDA-approved drugs.
