Common Signs Metformin Is Not Working and What to Do

Metformin is the most commonly prescribed drug used for the treatment of type 2 diabetes. Even so, not everyone responds to metformin in the same way, and, over time, the drug can start to lose its effectiveness and stop working entirely.

When used on its own, metformin is often extremely effective in controlling blood glucose (sugar). But, for most people, this effect will gradually wane, requiring the metformin dose to be increased or another diabetes drug to be added to the treatment plan.

This article explains how metformin works and signs that the drug may no longer be working. It also outlines some of the available options should metformin fail to control your blood sugar.

A person at a table with coffee and a blood sugar monitor - stock photo

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How Metformin Works

Metformin (sold under the brand names Fortamet, Glucophage, Glumetza, and others) is an oral drug used together with healthy eating, exercise, and weight loss to manage your blood sugar.

Its main function is to stop the liver from releasing too much glucose into the blood. The drug also helps increase your body’s response to insulin (the hormone made by the pancreas that helps your body utilize glucose for energy).

You can take metformin on its own or in combination with other diabetes medications, including insulin, to help treat type 2 diabetes. People with type 1 diabetes who have insulin resistance can also use it.

Benefits of Metformin

Metformin’s effectiveness, tolerability, safety, and ability to be combined with other diabetes medications make it the first-line drug of choice when treating people with type 2 diabetes.

Signs That Metformin Is Not Working

When taken as prescribed, metformin is highly effective at lowering blood sugar. Even so, you may experience occasional increases in blood sugar due to stress, a large meal, and other factors.

Most of the time, you don't need to worry about these occasional increases. It is only when you notice a pattern of high blood sugar (hyperglycemia) that you should speak with your healthcare provider.

The pattern may not be due to the waning effects of the drug. It could be that you are not following dietary guidelines, have stopped exercising, or have gained excessive weight. Or, it could be that you're not taking the drug as prescribed.

Whatever the reason, the very first indication that metformin is not working is when your blood glucose levels are high. You may only realize this when your hemoglobin A1C (a three-month average of blood sugar) is tested at your healthcare provider's office. Or, you may start to notice when using a blood glucose monitor.

You may also start to experience signs and symptoms of hyperglycemia, including:

  • Blurred vision
  • Fatigue
  • Frequent urination
  • Headache
  • Increased hunger
  • Increased thirst
  • Nausea or vomiting

When to Call Your Healthcare Provider

Sudden, unexplained increases in blood sugar that persist for several days may be a sign that your metformin is no longer working. Speak with your healthcare provider about whether your dose needs to be increased or if other diabetes medications are needed.

Why Metformin Failure Is a Concern

Metformin is prescribed because your healthcare provider believes that you need it to help control your blood sugar. It is often prescribed after lifestyle interventions (like diet, exercise, and weight loss) fail to provide glucose control.

If metformin is unable to control your blood sugar, you need to take action. In people with uncontrolled or poorly controlled diabetes, excessive accumulation of glucose in the bloodstream can cause progressive damage to blood vessels, nerves, and organs.

Among the possible complications of uncontrolled diabetes are:

What to Do If Metformin Isn’t Working

If metformin is not working as it should, there are different courses of action you may need to take depending on when the failure occurred.

If you just started taking metformin and don't see an improvement in your blood sugar after several weeks, contact your healthcare provider. You may not be taking the drug correctly, or your dose could be too low.

You should also let your healthcare provider know if you are not taking metformin as prescribed because of intolerable side effects like nausea and vomiting. They may be able to switch you to an extended-release version of metformin which may lessen your side effects.

If you have been taking metformin for several years and notice that your blood sugar is suddenly starting to rise, your healthcare provider may need to add another medication to your treatment plan. There is no standardized approach as to which drug should be added, but some of the more common options include:

  • Actos (pioglitazone)
  • DPP-4I inhibitors, including Januvia (sitagliptin), Tradjenta (linagliptin), Onglyza (saxagliptin), and Nesina (alogliptin) 
  • GLP-1 agonists, including Bydureon (exenatide), Byetta (exenatide, Saxenda (liraglutide), Mounjaro (tirzepatide), and Adlyxin (lixisenatide)
  • Injectable insulin
  • SGLT2 inhibitors, including Invokana (canagliflozin), Farxiga (dapagliflozin), Jardiance (empagliflozin), and Steglatro (ertugliflozin)
  • Sulfonylureas, including Amaryl (glimepiride), Glynase (glyburide), and Glucotrol (glipizide)

If metformin has stopped working, it is important to determine why and to work with your healthcare provider to get your blood sugar back under control. This can help avoid disease complications like heart disease, nerve damage, or eye damage.


Metformin is an oral diabetes medication that can help reduce blood sugar levels in people with type 2 diabetes. Although it is the most common drug used for the first-line treatment of type 2 diabetes, it doesn't work the same for all people and can begin to lose its effectiveness over time.

Unexplained increases in blood sugar may be the first sign that metformin has stopped working. You may also experience symptoms of hyperglycemia such as excessive thirst or hunger, fatigue, and blurry vision.

Whatever the cause of the treatment failure, action needs to be taken to restore glucose control and prevent diabetes complications. This may involve improving drug adherence, correcting dosing mistakes, increasing the metformin dose, or adding another diabetes drug to the treatment plan.

A Word From Verywell 

Metformin is not a "cure" for type 2 diabetes, and medication alone is not enough to keep your blood sugar in control. If you eat poorly or live an otherwise inactive lifestyle, metformin may only go so far in controlling your blood sugar.

No matter how early or advanced your diabetes is, good lifestyle choices are needed to ensure your long-term health and well-begin. This involves eating a healthy diet, exercising regularly, taking your medications as prescribed, and losing weight if you are overweight or have obesity.

If needed, ask your healthcare provider for a referral to a nutritionist or personal trainer who can help.

Frequently Asked Questions

  • Can metformin become less effective over time?

    Because diabetes is progressive, people may need a higher dose or additional medications the longer they have the disease. Metformin works best when combined with diet, exercise, and a healthy weight. Simply taking metformin without lifestyle changes will likely shorten the effectiveness of the drug.

  • What are common side effects of metformin?

    Common side effects of metformin include:

    • Heartburn
    • Bloating
    • Gas
    • Stomach pain
    • Metallic taste
    • Diarrhea
    • Constipation
    • Headache
    • Nausea or vomiting
  • When should you take metformin?

    Metformin is taken once or twice daily with food to avoid stomach upset and other gastrointestinal side effects. Ideally, the drug is taken with the morning meal for a once-daily dose and both the morning and evening meal for a twice-daily dose.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Barbie Cervoni MS, RD, CDCES, CDN
Barbie Cervoni MS, RD, CDCES, CDN, is a registered dietitian and certified diabetes care and education specialist.