Depending on the dosage, metformin may take 48 hours to 5 days to start working. If blood sugar levels remain high, the metformin may not be working, and doctors may recommend changing the treatment plan.

Metformin is an oral medication that can help treat type 2 diabetes alongside lifestyle changes. Diabetes is a chronic, progressive disease — it can get worse over time if a person does not receive treatment.

For people with type 2 diabetes who are making recommended changes to their diet and exercise routines, metformin can help lower blood sugar levels. There are several brand-name versions, including Glucophage.

This article describes what to do if it seems that metformin is not working.


In May 2020, the Food and Drug Administration (FDA) recommended that some makers of metformin extended release remove some of their tablets from the U.S. market. This is because an unacceptable level of a probable carcinogen (cancer-causing agent) was found in some extended-release metformin tablets. If you currently take this drug, call your healthcare provider. They will advise whether you should continue to take your medication or if you need a new prescription.

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Metformin does not instantly reduce blood sugar levels.

The effects are usually noticeable within 48 hours of taking the medication, and the most significant effects take 4–5 days to occur. However, the timing depends on the person’s dosage.

Other diabetes medications increase the amount of insulin in the body, and these can work faster to bring down blood sugar levels.

If metformin and changes to diet and exercise routines are not effective enough, the doctor may increase the dosage of metformin or prescribe additional medications.

Metformin works by:

  • lowering the amount of sugar that the liver produces
  • reducing the absorption of sugar throughout the intestines
  • improving how well the hormone insulin works

Metformin is only effective if a person also follows a recommended diet and exercise plan.

To check whether metformin is working, doctors encourage people to regularly monitor their blood sugar, or blood glucose, levels.

Learn about healthy blood glucose levels here.

To judge whether metformin is working as well as it should, a doctor may check the person’s levels of vitamin B12 and blood sugar.

Vitamin B12

Depending on the dosage, metformin may lead to a vitamin B12 deficiency. Other risk factors for this deficiency include:

  • having a plant-based diet
  • taking certain medications with metformin
  • having bariatric surgery, which can reduce the body’s ability to absorb this vitamin

If a doctor is concerned about the risk of a B12 deficiency, they may request more frequent checkups.

Blood sugar

Doctors also check levels of glycated hemoglobin (HbA1c). Levels of this protein can shed light on blood sugar levels over the past 2–3 months.

The test requires a blood sample from a vein, it is not a finger-prick glucose test.

For most people with diabetes, the target is an HbA1c reading of less than 7%. However, the goal varies, based on the person’s age and other factors.

If the HbA1c target is not reached, the doctor will adjust the diabetes treatment plan.

Learn more about the A1C test here.

Anyone who thinks that their treatment plan may not be working should let their doctor know.

A diabetes treatment plan can include lifestyle changes and medications. For a person with type 2 diabetes, metformin is only effective in combination with recommended changes to diet and exercise habits.

Some people with diabetes may be able to meet their blood sugar targets by combining dietary changes, regular exercise, and self-monitoring — without using medication. Other people require drug treatments.

Anyone who uses medications to control their blood sugar levels should:

Take medications as prescribed

Doctors typically prescribe metformin as a first-line treatment for type 2 diabetes and also recommend changes to diet and activity levels.

Metformin does not lower blood sugar levels instantly like insulin injections. It may take a few weeks or months for a doctor to be able to tell whether metformin is working.

Certain medications, including insulin and a group of drugs called sulfonylureas, can reduce blood sugar levels much more rapidly. However, a common side effect of sulfonylureas is low blood sugar, or hypoglycemia.

A doctor will provide clear instructions about how to take medication to maximize the benefits and minimize the risk of side effects. Taking medication in any other way can be extremely dangerous.


Exercise can increase sensitivity to insulin, which helps the body remove sugar from the blood more efficiently. Depending on factors such as the duration of the workout, the extra sensitivity can last for 24 hours.

Also, during exercise, muscle cells use sugar as fuel. If it is burning sugar in this way, the body does not need as much insulin to remove sugar from the blood.

Anyone who takes metformin needs to follow an approved exercise plan for the medication to have an effect.

Reduce the carbohydrate intake

Carbohydrates contribute to raising blood sugar. However, not all carbohydrates are bad for people with diabetes.

Foods that rank high on the glycemic index cause blood sugar levels to rise quickly, while foods that rank low have less drastic and immediate effects.

Diabetes Canada provide the following examples of carbohydrate-rich foods that rank low, medium, and high on the glycemic index.

Low glycemic index foodsMedium glycemic index foodsHigh glycemic index foods
Spelt breadWhite or whole wheat pita breadWhite or whole wheat bread
Steel cut oatsInstant, quick, or large flake oatsCertain breakfast cereals, like Corn Flakes
BarleyCouscousJasmine rice
Sweet potatoCooled potatoHot potato

Increase the dietary fiber intake

Doctors and nutritionists recommend that people with diabetes or who have a higher risk of the condition eat plenty of foods rich in dietary fiber, such as beans and other legumes.

This type of fiber is not digested in the small intestine and does not contribute to drastic increases in blood sugar like foods with lower fiber contents.

Discover 38 healthy high fiber foods here.

If metformin is not working, blood sugar levels can rise. This requires immediate medical attention.

High blood sugar

This issue does not always cause symptoms, but severely high blood sugar can cause:

Anyone who suspects that they have high blood sugar should receive medical attention right away.

Learn more about high blood sugar here.

As the American Diabetes Association caution, if blood sugar levels continue to rise, it can lead to diabetic ketoacidosis, also known as a diabetic coma.

Symptoms of diabetic ketoacidosis include:

Learn more about diabetic ketoacidosis here.

Metformin can cause minor side effects and some severe ones that require immediate medical attention.

Lactic acidosis

A rare but very serious side effect is lactic acidosis, or a buildup of acid in the blood. This can be fatal.

If a person notices the following symptoms, they should receive emergency medical attention:

Minor side effects

Metformin can cause some minor side effects. Common ones include:

Taking metformin with a meal may help ease these side effects. If they are mild but persist for a few weeks or longer, contact the doctor.

Metformin is a diabetes medication in a category of drugs called biguanides, but there are no alternatives for it in this class.

Other diabetes medications work in different ways. Beyond insulin and metformin, other drug treatments include:

  • Sulfonylureas: Examples include:
    • tolbutamide (Orinase)
    • glipizide (Glucotrol)
    • glyburide (Diabeta)
  • Meglitinides: Examples include:
    • repaglinide (Prandin)
    • nateglinide (Starlix)
  • Alpha-glucosidase inhibitors: Examples include:
    • acarbose (Precose)
    • miglitol (Glyset)
  • Thiazolidinediones: Examples include:
    • pioglitazone (Actos)
    • rosiglitazone (Avandia)
  • Glucagon-like peptide-1 agonist: Examples include:
    • exenatide (Byetta)
    • lixisenatide (Lyxumia)
    • liraglutide (Victoza)
    • albiglutide (Tanzeum)
    • dulaglutide (Trulicity)
    • semaglutide (Ozempic)
  • Dipeptidyl peptidase IV inhibitors: Examples include:
    • sitagliptin (Januvia)
    • saxagliptin (Onglyza)
    • linagliptin (Tradjenta)
    • alogliptin (Vipidia)
  • Selective amylinomimetic: pramlintide (Symlin)
  • Sodium-glucose transporter-2 inhibitors: Examples include:

Learn more about diabetes medications here.

Doctors choose the most appropriate diabetes medication for each person depending on their needs.

Some of these drugs are injected, and some people may prefer not to use them for this reason. The doctor will take these considerations into account.

The first-line treatment for type 2 diabetes is a combination of changes to diet and exercise routines and the medication metformin.

It may take several weeks or months before this treatment reduces blood sugar levels. Sulfonylureas and insulin can have faster results, but they can carry additional risks.

A doctor can provide detailed information about how diabetes medications work and other ways to reduce blood sugar levels.

Severely high blood sugar is a medical emergency, so it is important to undergo regular monitoring and understand when to seek medical care.