Metformin dosage: what is the right dose for me?

Metformin (or metformin hydrochloride) is commonly given to people with type 2 diabetes mellitus to help lower blood sugars. Your metformin dose will take into account many different factors, such as your age, weight, other medical conditions, and lifestyle.

Glucophage is a brand name version of metformin. Other brand formulations include Fortamet, Riomet, and Glumetza. This medicine is available as a tablet, liquid, or in an extended-release (ER) dosage form. 

The immediate-release tablets and liquids are usually taken twice a day, whereas you take the extended-release formulations once daily (usually with your evening meal). In most cases, your healthcare provider will often start you on a low dose and gradually build up to the strength that best controls your blood sugars to minimize side effects (UpToDate, n.d.). 

Most people take metformin at night, but the most important thing is to stay consistent from day to day—take your medication around the same time each day.

The immediate-release tablets come in 500 mg, 850 mg, and 1,000 mg strengths, and the extended-release tablets are available in 500 mg, 750 mg, and 1,000 mg doses. A typical metformin dose for a person with type 2 diabetes ranges from 500 mg to a maximum dose of 2550 mg a day to be taken with food to help avoid stomach upset (UpToDate, n.d.). Then, based on blood test results measuring elements such as blood sugar levels and hemoglobin A1C (HbA1C), your healthcare provider may keep adjusting your daily dose over time.

It's all about how your particular blood sugar levels respond. As mentioned, gradually increasing the dose may reduce side effects such as diarrhea and other side effects. 

Always take your medication as prescribed and as directed by your pharmacist and healthcare provider. If you miss a dose of metformin, don't double up next time. And if you're bothered by diarrhea or other common side effects such as abdominal pain and nausea, remember these usually resolve within a few weeks after adjusting your daily dose. Don't just stop metformin on your own without talking to your healthcare provider (MedlinePlus, 2020).

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Metformin is one of the most widely used diabetes medications; it belongs to the biguanide class of diabetes drugs (Wang, 2014). It is FDA-approved as a type 2 diabetes treatment and the drug's ability to help control blood glucose (sugar) levels in type 2 diabetes. This may also explain the use of metformin for other "off label" conditions (not FDA-approved for these conditions), including (UpToDate, n.d.): 

• Gestational diabetes: diabetes during pregnancy

• Polycystic ovary syndrome (PCOS): a hormonal imbalance in women that causes irregular periods, weight gain, facial hair growth, and insulin resistance

• Prediabetes: high blood sugar levels, but not high enough to be diagnosed with diabetes

• Weight gain from antipsychotic medicines like clozapine and olanzapine: medications used to treat schizophrenia and schizoaffective disorder.

In type 2 diabetes, your blood sugar levels get too high (hyperglycemia) because either your body doesn't produce enough insulin—the hormone that controls blood sugar levels—or the body doesn't respond to the insulin it does make. The hyperglycemia that results can cause damage to your nerves, eyes, kidneys, and blood vessels and is a risk factor for the development of cardiovascular disease.

According to the American Diabetes Association (ADA), if you are diagnosed with type 2 diabetes, your healthcare provider will likely prescribe metformin along with instructions on getting regular physical activity and eating a healthy diet (ADA, 2020). The goal is to help you regulate and gain control over your blood glucose levels and prevent harm to vital organs, like your kidneys, eyes, and heart. 

Like type 2 diabetes, metformin can help pregnant women treat their gestational diabetes, typically during the 2nd and 3rd trimesters. Metformin is used as gestational diabetes treatment when a healthy diet and lifestyle changes are not enough. While gestational diabetes usually goes away after giving birth, it does increase the chance of developing type 2 diabetes later on in life (Balsells, 2015). 

With PCOS, there is a hormonal imbalance in male and female hormones in women, leading to irregular periods, weight gain, facial hair growth, and insulin resistance. Metformin may help address the insulin resistance, which research suggests may be at the heart of this disorder. By increasing insulin sensitivity, metformin can not only lower blood sugar levels but may also help women with PCOS lose weight and improve overall symptoms (Banaszewska, 2019).

Metformin can also prevent people with prediabetes from getting worse and developing into full-blown type 2 diabetes. Prediabetes is a condition where you have elevated blood sugar levels but not high enough to meet the criteria for type 2 diabetes. 

The ADA recommends using metformin, along with increased physical activity and a healthy diet, to treat prediabetes in people at a high-risk for developing diabetes. These high-risk groups include people with prediabetes who are under 60 years of age, have a body mass index (BMI) of 35 kg/m or greater, or who had gestational diabetes during pregnancy (ADA, 2019).

Researchers have pointed to a large amount of evidence showing that metformin is safe and even cost-effective at various dosages for preventing and delaying the development of type 2 diabetes (Moin, 2018). 

Lastly, people with schizophrenia and schizoaffective disorder are often started on antipsychotic medications, like clozapine and olanzapine, in addition to other therapies. These medications generally cause weight gain, which can be prevented by giving people metformin. By avoiding weight gain, you can also prevent obesity and an increased risk of heart disease (de Silva, 2016). 

Most people do well with this medicine, which is considered safe and effective for type 2 diabetes (DPP Research Group, 2012). The most common problem people experience is diarrhea (up to half of people taking metformin have this), especially when starting or increasing metformin (DailyMed, 2017). Nausea, vomiting, and pain around the abdominal area can happen, too. Experts recommend taking the medicine with food to lessen these side effects. Ask your healthcare provider or pharmacist for instructions.  

If you've taken metformin for many months or years, your healthcare provider may also check your vitamin B-12 levels from time to time as metformin can lead to low absorption of this nutrient and, potentially, vitamin B-12 deficiency (DailyMed, 2017).

While metformin is considered safe, there are some severe side effects to consider. Some people may find that they develop low blood sugars, a condition called hypoglycemia. You are at a higher risk of this happening if you take other medications, like insulin, that also lower your blood sugars. 

More severe, much more rare, is the adverse effect of lactic acidosis. The U.S. Food and Drug Administration (FDA) has issued a black box warning regarding metformin causing lactic acidosis. Lactic acidosis is a buildup of lactic acid; this condition is rare, affecting just 1 in 30,000 people a year. It is more likely to occur in people who have kidney or liver problems or excessive alcohol use (Wang, 2017). Lactic acidosis is a medical emergency requiring prompt medical attention. 

People often do lose weight while on metformin, probably as a result, among other things, of its effect in dampening appetite (DPP Research Group, 2012). Meanwhile, other diabetes medicines have been linked to the reverse effect of weight gain or plateau.

You shouldn't take metformin if you have liver disease or poor renal function (kidney disease), type 1 diabetes, or if you've had lactic acidosis while taking metformin. 

If you need an imaging procedure or radiology study with intravenous contrast, like a CT scan, you should temporarily stop your metformin (with guidance from your healthcare provider); this can help prevent kidney problems. Also, people with liver disease, in general, should avoid using metformin because it increases your risk of developing lactic acidosis (DailyMed, 2017). 

• Food interactions. There are no food interactions with metformin; make sure you are eating a healthy diet. If you're not sure how to do this, ask your healthcare provider for a referral to a nutritionist. 

• Alcohol interactions. Watch your alcohol intake, and don't drink heavily while taking metformin. When you do this, there's an increased risk of lactic acidosis.

• Drug interactions. Taking certain other medicines that can change blood sugar levels can cause problems when you also take metformin: other diabetes medicines (like sulfonylureas), blood pressure-lowering drugs (like calcium-channel blockers), prednisone, diuretics, estrogens, and asthma and cold medications (DailyMed, 2017). 

Whether you have prediabetes or diabetes, stick to a schedule with metformin. Do what you need to remember to take it every day, around the same time, so that the dosage you've been prescribed can do its important work of keeping your blood sugar well-controlled. If you skip or regular miss doses, your blood sugar can rise, causing health complications down the road. 

Ultimately, taking metformin involves a long-term relationship and good communication with your healthcare provider over months or years. Blood tests, like hemoglobin A1C (HbA1C), can give you and your provider information on whether your blood sugar is in the right range. 

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Current version

October 14, 2020

Written by

Andrea Pierce

Fact checked by

Chimene Richa, MD

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About the medical reviewer

Chimene Richa, MD

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.