What to Know About Metformin

An Anti-Diabetes Medication Approved to Manage Glucose

In This Article

Metformin (brand names Glucophage, Riomet, Fortamet, Glumetza, and Glucophage XR) may be prescribed by your doctor to help manage blood sugar levels in diabetes or another related condition.

It's important to understand how metformin works in the body to help manage diabetes, and what you can do to help the drug be an effective treatment.


Metformin belongs to a class of drugs called biguanides, which are derived from the French lilac flower. Metformin helps to lower blood sugar by utilizing insulin and reducing insulin resistance (making your body more sensitive to insulin).

According to the American Diabetes Association Standards of Care, metformin, if tolerated, is the preferred initial oral diabetes medication for type 2 diabetes because it is considered the most effective. Unlike people with type 1 diabetes, people with type 2 still produce ​insulin (although insulin production may decrease as the disease progresses). The problem is that they are either not making enough insulin or the insulin they do make isn't being used efficiently.

Metformin helps to balance blood sugar in three ways: by reducing the amount of glucose absorbed from food, by lowering glucose produced by the liver, and by increasing the body's insulin sensitivity.

Many people with type 2 diabetes may carry excess weight—fat cells prevent insulin from doing its job, ultimately causing the cells to become resistant to insulin. When cells become resistant to insulin, insulin is unable to direct sugar (glucose) from the bloodstream to the cells to use for energy, and instead, the sugar remains in the blood.

As a result, the liver responds by making more sugar because it thinks the cells need it for fuel, and then the pancreas responds by making even more insulin. You wind up with chaos—high blood sugars and high insulin levels. Metformin helps to restore normalcy by increasing insulin sensitivity and reducing the production of glucose made by the liver.

Off-Label Uses

In addition to being used for diabetes, metformin is sometimes used "off-label" in polycystic ovary syndrome (PCOS) as an aid in fertility, as a weight-loss adjunct, to treat gestational diabetes, or in HIV lipodystrophy syndrome.

Research is currently evaluating the possible increased survival of those with several cancers such as lung cancer, breast cancer, and bladder cancer who have been treated with metformin. Other studies have found that metformin targets many pathways in the growth of cancer. Metformin is also being studied for its effect on the thyroid, as it appears to reduce the risk of goiters, thyroid nodules, and thyroid cancer.

Before Taking

To assess if you're a good candidate for metformin, your doctor will test your blood glucose and A1c levels to get a range of your current blood sugar control. As metformin is typically the first line of defense when treating type 2 diabetes (in addition to diet and lifestyle modifications), you may start out on a low dosage with regular monitoring to see if your glucose control improves.

Precautions and Contraindications

Metformin does not directly reduce blood sugar in the same manner as insulin. Therefore, it is not appropriate for people with type 1 diabetes who require insulin.

Additionally, people with kidney disease or kidney failure should not take metformin. It is also not recommended for children under age 10. Children under 17 should not take the extended-release formula.

Usage during pregnancy may be acceptable, however, metformin has been shown to enter breast milk and may not be suitable for nursing mothers.


Metformin is a medicine that should be increased or titrated gradually to ease any stomach discomfort when it is first started. How long this takes will depend on what your health care provider prescribes and how you respond to the medication.

For example, a person who is new to metformin and has been prescribed 2000 milligrams (mg) twice a day may start by taking 500 mg once daily with dinner for one week. At week two, they will take 500 mg with breakfast and 500 mg with dinner. At week three, they will take 1000 mg with dinner and 500 mg with breakfast. And at week four, they will meet their therapeutic goal—taking 1000 mg with breakfast and 1000 mg with dinner.

Throughout the duration of titration, your doctor may ask you to monitor your blood sugar. If you experience low blood sugar or any other side effects, contact your health care provider so that the medication could be adjusted accordingly.

If you miss a dose, try to take the missed pill as soon as possible, unless you're approaching the time of your next regular dose.

Doubling up on the medication dose or overdosing may result in hypoglycemia. Signs of hypoglycemia include dizziness, shakiness, sweating, confusion, numbness or tingling around the mouth and should be treated immediately by a healthcare provider.


Your dosage may need to be modified by your physician if you have pre-existing liver or kidney issues. In these cases, your symptoms and blood markers should be closely monitored.

How to Take

It is recommended that people take metformin with meals as this both increases its absorption in the stomach and reduces side effects—stomach cramps, diarrhea, and nausea. Typically, most people new to metformin will take it with the largest meal. To remember to take metformin, you should try to take it around the same time(s) every day.

Generally, try to avoid skipping meals and drinking alcohol while taking this medication.

Side Effects

As with taking any medication, the potential side effects must be weighed against the potential benefits. In the case of metformin, the side effects are fairly innocuous.


The biggest complaint people have about metformin is that it causes gas and diarrhea. This can often be reduced by increasing the dose gradually. If you do experience diarrhea or gas, make sure to contact your healthcare provider to make sure you are taking the medication correctly.

If you are experiencing persistent side effects such as gas or diarrhea, ask your healthcare provider about the extended-release version of this medicine—it is a time-released version of the medicine which may help to prevent the gastrointestinal side effects. The extended-release version is usually taken once per day with the evening meal.

Unlike many treatments for diabetes, metformin does not typically cause hypoglycemia (low blood sugar.) Also, unlike many type 2 diabetes medications, Metformin does not cause weight gain and may even assist with weight loss.

Other common side effects include:

  • Nausea
  • Vomiting
  • Weakness
  • Metallic taste in the mouth


Some side effects of metformin can be more serious. One of these effects is lactic acidosis.  Though the latest studies suggest this is an uncommon condition which may not be directly associated with metformin, the risk of lactic acidosis is increased in both those with chronic kidney disease and those with liver disease.

Lactic acidosis occurs when lactic acid builds up in the blood and is caused by the body having to metabolize sugars without the presence of oxygen instead of aerobically. People not on metformin may develop lactic acidosis from vigorous exercise, serious illness, injury, or drug toxicity.

Symptoms of lactic acidosis related to metformin may be mild or severe and can include shortness of breath, swelling, weakness, and muscle pain. If you experience these symptoms while taking metformin you should seek medical help right away.

If lactic acidosis goes untreated, it may result in severe complications or even death (cardiac arrest).

Metformin may also result in a B12 deficiency, a complication known as pernicious anemia and can lead to permanent neurological damage. B12 deficiency is also linked with an increased risk of strokes. Early symptoms of B12 deficiency may include anemia, ringing in the ears, and depression. For those using metformin, it is important to have your B12 levels monitored so a lack of the vitamin can be addressed before a deficiency occurs.

Warnings and Interactions

Metformin may interact with numerous medications, which may affect how either medication functions.

Serious interactions may occur when using metformin and:

  • Anti-diabetes medications such as gymnema and gatifloxacin
  • Iodinated contrast materials (used in CT scans)

Stop taking metformin 48 hours before any dental or surgical procedures and before receiving any iodinated contrast, typically used in CT scans.

If you're taking beta-blockers (such as metoprolol or propranolol) at the same time as metformin, the beta-blockers may prevent the fast heartbeat you typically feel when your blood sugar drops too low, virtually eliminating that warning sign.

Tell any doctor or dentist you're seeing that you're taking metformin. Metformin may also be combined with other diabetes medicines:

  • Actoplus Met (containing Metformin, Pioglitazone)
  • Avandamet (containing Metformin, Rosiglitazone)
  • Glucovance (containing Metformin, Glyburide)
  • Invokamet (containing Metformin HCl/Canagliflozin)
  • Janumet (containing Metformin, Sitagliptin)
  • Janumet XR (containing Metformin, Sitagliptin)
  • Jentadueto (containing Metformin, Linagliptin)
  • Kazano (containing Metformin/Alogliptin)
  • Kombiglyze XR (containing Metformin, Saxagliptin)
  • Metaglip (containing Metformin, Glipizide)
  • Prandimet (containing Metformin, Repaglinide)
  • Synjardi (containing Metformin, Jardiance)
  • Xi Guo XR (containing Metformin HCl, Dapagliflozin)

May 28, 2020: The Food and Drug Administration (FDA) has requested that manufacturers of certain lots of metformin voluntarily withdraw the product from the market after the agency identified unacceptable levels of N-Nitrosodimethylamine (NDMA). Patients should continue taking their medications as prescribed until their health professional prescribe an alternative treatment, if applicable. Stopping metformin without a replacement can pose serious health risks to patients with type 2 diabetes.

A Word From Verywell

While metformin is an excellent choice in addressing type 2 diabetes, lifestyle approaches such as a healthy diet and weight reduction (in those who are overweight) are the most important ways to address insulin resistance and avoid the possible long-term consequences of diabetes.

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