What is Metformin?
Metformin is a prescription drug used to treat type 2 diabetes, which is characterized by high blood sugar levels. While metformin doesn’t cure diabetes (currently, there is no cure for diabetes), it helps people living with type 2 diabetes maintain safe blood sugar levels.
Metformin is an oral medication, so it usually comes as a tablet you swallow with water. It consists of metformin hydrochloride, which is the medication itself, in addition to some inactive ingredients that help with the drug's stabilization and delivery.1
The U.S. Food and Drug Administration (FDA) has approved metformin for treating type 2 diabetes, but this drug can still be prescribed off-label for people living with type 1 diabetes. Type 1 diabetes, an autoimmune disease that prevents the pancreas from producing insulin, requires insulin replacement therapy to regulate blood sugar levels. In some cases, metformin may be prescribed alongside insulin therapy to help people living with type 1 diabetes who are overweight manage their insulin resistance. Also, metformin is sometimes prescribed to help manage gestational diabetes and polycystic ovary syndrome (PCOS).2
Metformin Drug Class and Names Variations
Metformin belongs to a class of drugs called biguanides, which is a fancy way of saying that they help lower blood glucose. Metformin is the only biguanide drug currently on the market, and it's available in other brand names, including:
- Glucophage XR
- Riomet ER
What is Metformin Used For, and How Does it Work?
Metformin is used to both treat and prevent type 2 diabetes. It's also used to treat gestational diabetes, which can affect both the mother and baby. Metformin is often prescribed for polycystic ovary syndrome. However, it hasn't officially been approved as a PCOS treatment by the FDA, so using it for this condition is considered off-label.
Metformin works by helping your liver produce less glucose, but it also helps lower the amount of glucose you absorb from food while increasing your natural response to insulin (the hormone that controls the amount of glucose in the blood). Simply put, metformin helps people with high blood sugar lower their blood glucose levels to an optimal, safe range.3
Some research also suggests metformin is linked to protecting against cancer and heart disease in people living with type 2 diabetes.4
13 Common Side Effects of Metformin
The common side effects of metformin are generally mild and tend to occur when you first begin taking the medication. In other words, the side effects typically subside as you continue treatment.
Common side effects
The common side effects are mild and occur in about 1 in 100 people. So if you do experience side effects from the drug, it'll likely be one or more of the following:
- Stomach pain
- Weight loss
- Loss of appetite
- Weakness or fatigue
- An unusual metallic taste in the mouth
Serious side effects
While some cases of more severe side effects require medical attention, they're very rare and occur in less than 1 in 10,000 people. Some of the more serious side effects include:
- Lactic acidosis (or lactic acid build-up in the body)
- Anemia (or low red blood cell count)
- Hypoglycemia (or low blood sugar)
- Vitamin B12 deficiency
Call your doctor or contact 911 immediately if you experience any of the following side effects:
- Severe tiredness
- Fast or shallow breathing
- Slow heartbeat
- Whites of the eyes or the skin turn yellow5
Who Should Avoid Metformin
Not everyone is a good candidate for metformin. Your doctor may not prescribe you metformin and might suggest a different drug instead if you have any of the following conditions:
- An allergic reaction to metformin or other medicines
- Liver disease or kidney problems
- A severe infection
- A recent heart attack or heart failure
- Breathing or blood flow problems
- Drink a lot of alcohol
Metformin Side Effects in Women
If you and your baby are healthy, taking metformin while pregnant or breastfeeding is considered safe, even if you're taking insulin.
Research shows pregnant women may experience mild, stomach-associated side effects, such as nausea, vomiting, and diarrhea, more often while on metformin. But it's worth noting that these side effects are manageable.6,7
And here's a bit more reassurance: while metformin is transferred in small amounts into breast milk, research shows the drug hasn't been associated with any side effects in breastfed infants.
How to Stop Metformin Side Effects? 4 Tips
Many of metformin's common side effects affect the digestive system, and luckily enough, they are manageable with a few simple tricks. The way you take the drug can affect whether you get side effects, so try the following:
Begin with a low dose
You'll typically start with a daily dose of 500 milligrams. Beginning with a low dose of metformin and gradually increasing it over time can help minimize any side effects.
Use metformin with food
Food slightly delays the drugs' absorption, so taking metformin with breakfast, lunch, or dinner can help reduce your chances of an upset stomach, a common side effect of metformin. However, metformin on an empty stomach is still considered safe.
Switch to extended-release metformin
Extended-release tablets (sometimes called "slow-release") release the drug into your bloodstream gradually, so you'll need to take fewer tablets daily. Extended-release metformin is associated with fewer side effects.
Take metformin tablets whole
Never cut or crush your metformin tablets, as doing so can cause your body to absorb the drug too fast, which can lead to more side effects. If you have trouble swallowing the pills whole, talk to your doctor about switching to metformin liquid or sachets instead of tablets.
Metformin pills are available in either standard or slow-release tablets, but the medication is also in liquid and sachet form. Whichever type you go with, the recommended dosage usually starts at 500 milligrams.
The maximum daily dose of metformin is 2,000 milligrams, which can be achieved by taking four 500-milligram tablets daily. Liquid metformin is taken in 5-milliliter doses, available in strengths of 500 milligrams, 850 milligrams, or 1,000 milligrams. Sachets of metformin are available in doses of either 500 milligrams or 1,000 milligrams.
There's no need to memorize any of this; if you're prescribed metformin, you'll work with your doctor to figure out a dosage that's right for you.8
Potential Metformin Drug Interactions
Metformin may interact with some medications, including:
- Steroids such as prednisolone
- Diuretics such as furosemide
- Medicines that treat heart problems and high blood pressure
- Male and female hormones, such as testosterone, estrogen, or progesterone
- Other diabetes medicines
Always tell your doctor about any vitamins, supplements, and herbal remedies you're on before starting metformin (or any other medication, for that matter).
If you drink alcohol, discuss with your doctor if you're planning to take or are already on metformin. That's because drinking alcohol while on metformin can raise your risk of low blood sugar (clinically known as hypoglycemia) and lactic acidosis (lactic acid build-up in the blood).9
You'll also want to pay attention to your hydration levels when you're on metformin. Dehydration can cause acute kidney failure, which could lead to the accumulation of metformin in the body (since the kidneys remove metformin from the body). Too much metformin in your body can increase your risk of developing lactic acidosis, so stay well-hydrated while on metformin.10
Signs of lactic acidosis include nausea, vomiting, fatigue, fast and deep breathing, muscle cramps, body aches, drowsiness, confusion, lack of coordination, and low urine output. Seek medical attention immediately if you experience any of these symptoms.11
Learn More About Diabetes and Managing Blood Sugar Levels with Signos’ Expert Advice.
Before taking any medication, including metformin, it's important to talk to your doctor about potential side effects to help you understand the possible risks and benefits of the drug. Always discuss medication side effects, risks, and benefits with your doctor. Signos is here to help you get all the information you need, so you're equipped with prior knowledge before that doctor's visit.
Signos' continuous glucose monitors (CGMs) help you better understand what affects your blood sugar levels — and how — so you can take control of your health. By logging your food intake with Signos, you can easily track your glucose levels, identify foods that cause spikes, and get exercise recommendations to lower your blood glucose levels. And you can learn even more about blood sugar levels and managing diabetes on Signos’ blog.
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People Also Ask:
What are the toxic side effects of metformin?
Some of the more severe side effects of metformin include severe tiredness, fast or shallow breathing, slow heartbeat, and the whites of the eyes or the skin turning yellow. Call your doctor or 911 immediately if you experience these side effects.
What should you avoid while taking metformin?
Avoid drinking too much alcohol while taking metformin because alcohol can raise your risk of hypoglycemia (low blood sugar) and lactic acidosis (lactic acid build-up in the blood).
Why do doctors no longer prescribe metformin?
Metformin is still prescribed by doctors; it's the most common medication used to treat type 2 diabetes. However, if you have serious kidney disease, your doctor may not prescribe you metformin, as the drug can contribute to lactic acidosis.
What is the most serious adverse reaction of metformin?
While uncommon, lactic acidosis is metformin's most severe side effect. This is considered a "boxed warning," as the FDA requires metformin manufacturers to print a warning notifying users about this risk on the drug's label. Seek medical attention immediately if you experience any symptoms of lactic acidosis, such as nausea, vomiting, fatigue, fast and deep breathing, muscle cramps, body aches, drowsiness, confusion, lack of coordination, or low urine output.
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Topics discussed in this article:
- Metformin Hydrochloride. (n.d.). https://rb.gy/k2cpo
- What role for metformin in type 1 diabetes? (2018). Drug and Therapeutics Bulletin, 56(7), 78–80. https://doi.org/10.1136/dtb.2018.7.0645
- Metformin: MedlinePlus Drug Information. (2020, March 15). https://medlineplus.gov/druginfo/meds/a696005.html
- Stevenson-Hoare, J., Leonenko, G., & Escott-Price, V. (2023). Comparison of long-term effects of metformin on longevity between people with type 2 diabetes and matched non-diabetic controls. BMC Public Health, 23(1). https://doi.org/10.1186/s12889-023-15764-y
- Side effects of metformin. (2022, March 22). United Kingdom National Health Service. https://www.nhs.uk/medicines/metformin/side-effects-of-metformin/
- Pregnancy, breastfeeding and fertility while taking metformin. (2022, March 22) United Kingdom National Health Service. https://www.nhs.uk/medicines/metformin/pregnancy-breastfeeding-and-fertility-while-taking-metformin/
- Hyer, S., Balani, J. P., & Shehata, H. (2018). Metformin in Pregnancy: Mechanisms and Clinical Applications. International Journal of Molecular Sciences, 19(7), 1954. https://doi.org/10.3390/ijms19071954
- How and when to take metformin. (2022, March 22). United Kingdom National Health Service. https://www.nhs.uk/medicines/metformin/how-and-when-to-take-metformin/
- Taking metformin with other medicines and herbal supplements. (2022, March 22). United Kingdom National Health. https://www.nhs.uk/medicines/metformin/taking-metformin-with-other-medicines-and-herbal-supplements/
- Scheen, A. (2011). Metformin and lactic acidosis. PubMed, 66(5), 329–331. https://doi.org/10.2143/acb.66.5.2062583
- Lactic Acidosis. (2023, June 13). Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/25066-lactic-acidosis