Metformin for Prediabetes: Is It Safe to Use?

By Robynn Lowe
Medically reviewed checkmarkMedically reviewed
July 22, 2022

Metformin is a medication that is used to treat type 2 diabetes mellitus. Some healthcare providers and the American Diabetes Association (ADA) also recommend metformin for prediabetes.

Prediabetes is when blood sugar levels are higher than normal, but not high enough to be diagnosed with type 2 diabetes.

In this article, we’ll discuss why metformin may be used for prediabetes, how to safely take it, and possible short and long-term effects. 

Metformin for Prediabetes

Prediabetes can usually indicate an increased risk for developing type 2 diabetes. Some healthcare providers treat prediabetes conditions to help prevent the onset of type 2 diabetes. 

Treating prediabetes is also important because it can increase the risk for cardiovascular disease (CVD).

The criteria for having prediabetes are:

  • Fasting blood sugar level of between 100-125 mg/dL
  • Hemoglobin A1C (HbA1C) between 5.7-6.4%

In many cases, prediabetes can be reversed with diet and lifestyle changes, like regular physical activity. Diet and exercise alone decrease the risk of getting type 2 diabetes by 58%.

In some cases, dietary changes and exercise alone don’t make enough difference.

In this case, a medical provider may prescribe metformin to help improve how the body handles blood glucose and responds to insulin.

Not everyone will need metformin for prediabetes. People who are at higher risk for developing type 2 diabetes or who have more risk factors may benefit from metformin therapy. Risk factors include:

  • Having a higher body mass index (BMI)
  • Prior gestational diabetes

Metformin prevents the liver from making more glucose and increases the body’s sensitivity to insulin, which takes glucose out of the blood and into cells.

Metformin also changes the way that glucose is absorbed in the intestines.

Metformin may be prescribed in immediate release or extended release versions. Dosages usually start low and gradually increase to minimize side effects.

It is available as a generic or as brand names Glucophage, Fortamet, or Glumetza.

Guidelines for the use of Metformin to Treat Prediabetes

Because the FDA has not approved metformin for the treatment of prediabetes, healthcare providers follow the guidance of the American Diabetes Association (ADA). Metformin is their only approved treatment for prediabetes.

There is some disagreement among healthcare providers and researchers about using metformin for prediabetes.

According to research, there are reasons to treat and reasons not to:

  • Reasons not to treat prediabetes: Some researchers consider the link between high blood glucose levels and cardiovascular disease to be weaker than other risk factors. Metformin can only treat high glucose and does not address other heart disease risk factors. Around ⅔ of people who have prediabetes do not go on to get type 2 diabetes, and around ⅓ of people return to completely normal glucose balance. In this case, researchers suggest close monitoring of people who meet the prediabetes criteria, as well as people with a history of gestational diabetes. If they progress to diabetes, then metformin should be started right away.
  • Reasons to treat prediabetes: Other researchers consider early intervention of prediabetes to be essential for preventing type 2 diabetes complications that can be happening for years before a clinical diagnosis of diabetes is made. By using metformin in prediabetes, damage caused by high glucose levels to microvascular and neuropathic function, along with cardiovascular risk, could be delayed or prevented. This could improve quality of life in the long-term.

A healthcare provider will ultimately consider the individual needs and those who are at the highest risk before deciding to treat prediabetes conditions.

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What to Avoid When Taking Metformin

If you take metformin, there are some potential interactions to be aware of.

Tell your doctor or pharmacist about all of the medications, OTC medicines, and dietary supplements that you take.

Metformin interacts with the following:

  • Beta blockers
  • Cimetidine
  • Calcium channel blockers
  • Chromium
  • Coenzyme Q10
  • Corticosteroids
  • Diuretics
  • Digoxin
  • Dofetilide
  • Estrogens
  • Garlic
  • Green tea
  • Morphine
  • Oral contraceptives
  • Phenytoin
  • Phenothiazines
  • Procainamide
  • Quinidine
  • Ranitidine
  • Sympathomimetics
  • Triamterene
  • Vancomycin

If you have surgery or a radiology procedure coming up, you will stop metformin before them, since it interacts with iodine contrast dye and other medications used for these procedures.

When Should You Take Metformin

Metformin should be taken with meals to reduce the chance of gastrointestinal side effects like nausea, bloating, and diarrhea.

When Should You Avoid Taking Metformin

Even if you are prescribed metformin, make sure your doctor knows if you ever have any of the following conditions, as it may change your dosage requirements or you may need to stop taking metformin until the condition improves:

  • Serious infections
  • Severe diarrhea
  • Severe or frequent vomiting
  • Fever
  • Dehydration
  • Drinking large amounts of alcohol

Long- and Short-Term Effects of Metformin

Short-term side effects of metformin usually improve over time as the body adjusts to the medicine. They include:

Long-term effects of metformin may include the potential to develop anemia. Metformin makes it harder to absorb vitamin B12, which can lead to B12 deficiency. 

In some cases, this can decrease the number of red blood cells and cause anemia. Signs include extreme tiredness, brain fog, and dizziness

It can be treated with vitamin B12 supplements, iron supplements, or dietary changes.

Other Uses for Metformin

Metformin is approved by the FDA for the treatment of type 2 diabetes. It may also be used for type 2 diabetes, prediabetes, and insulin resistance.

Risk and Precautions

In some cases, metformin should be avoided as it could cause serious interactions or health problems.

Metformin has a black box warning from the FDA because in rare cases it can cause a build up in the body of lactic acid that, left untreated, may be fatal.

Metformin may also not be safe for:

  • People who have kidney disease
  • People over age 65
  • People with a history of heart attack or stroke
  • People who have a history of diabetic ketoacidosis
  • People who have ever been in a coma
  • People with a history of heart disease or liver disease

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When to See a Medical Provider

Metformin is not always prescribed for prediabetes, even if you meet the American Diabetes Association criteria. It also does not replace the need for dietary and lifestyle intervention to prevent type 2 diabetes.

If you have prediabetes and are struggling to maintain normal glucose or HbA1c levels on your own with diet and physical activity, ask your healthcare provider if metformin or other medication could help.

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Frequently Asked Questions

What is the best medication for prediabetes?
As of now, the FDA has not approved any medications to treat it. The American Diabetes Association has only approved metformin for treating prediabetes.
How quickly does metformin lower A1C?
A meta-analysis of nearly 8,000 patients on metformin found that it can reduce hemoglobin A1C levels by just over 1% in less than 24 weeks. How quickly it works depends on a person’s individual health factors, diet, lifestyle, and other medical conditions.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Robynn Lowe

Robynn Lowe is a board certified Family Nurse Practitioner with over 15 years in the medical field. Robynn received her Bachelor's and Master's degrees from Florida Atlantic University and has been practicing in rural family medicine since. Robynn is married to her college sweetheart, Raymond and they have three awesome children. When Robynn isn't with patients you can find her shopping, coaching her kids sports teams, or spending time on the water.

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