What to know about the biguanide (metformin)

Biguanides are a class of drugs used to treat type 2 diabetes and other diseases. They work by reducing the production of glucose during digestion.

Metformin is currently the only biguanide drug available for the treatment of diabetes in most countries. Glucophage (metformin) and Glucophage XR (metformin extended-release) are well-known brands of these drugs. Others include Fortamet, Glumetza and Riomet. Metformin can also be used in combination with several other diabetes medications, such as sulfonylureas.


Metformin is often used to treat type 2 diabetes once the disease cannot be controlled with lifestyle changes alone. If you are diagnosed with type 2 diabetes and need medication, metformin may be the first medication you will take. As diabetes progresses, insulin injections may be required to control blood sugar, but metformin may be continued to enhance the body’s ability to use insulin.

The American Diabetes Association (ADA) guidelines for the treatment of type 2 diabetes recommend that people with certain high-risk factors, including cardiovascular and kidney problems, start taking metformin and other therapies that have proven cardiovascular benefits to help improve outcomes. Your healthcare provider will review your medical history to determine if you fall into this category.

Metformin works by controlling the amount of sugar in the blood. It doesn’t affect how much insulin your body produces, but it increases insulin sensitivity. This helps your cells absorb glucose for energy, reduces glucose production in your liver, and lowers the concentration of glucose in your blood.

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Other types of biguanides

Biguanides originally came from the French clove, also known as goat rue (Guava). Some herbs may include this plant. If you are taking diabetes medication, tell your healthcare provider about any herbal supplements you are taking to avoid interactions.

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Phenformin was introduced at the same time as metformin in 1957, but was subsequently withdrawn in the late 1970s because of its association with a fatal risk of lactic acidosis. Buformin was developed in Germany in 1957, but was never sold in the United States. It has also been found to lead to an increased risk of lactic acidosis. These forms of biguanides may still be available in some countries.

Other types of biguanides, called proguanil and proguanil, are used as antimalarial drugs.

Off-label use

Metformin may occasionally be prescribed off-label for type 1 diabetes, obesity, and polycystic ovary syndrome (PCOS). It is also being studied for potential anticancer and cardioprotective benefits.

Metformin: an effective treatment for type 2 diabetes

Before taking

In addition to standard testing for diabetes, your healthcare provider will also test your kidney function to estimate glomerular filtration rate, or eGFR, before you first prescribe metformin.

Precautions and contraindications

According to the ADA treatment guidelines, people with advanced kidney disease should not take metformin. However, in people with mild renal insufficiency and some people with moderate renal function, there is now substantial evidence that the combination of metformin and careful monitoring is beneficial.

If you drink regularly or tend to drink heavily at one time, share this information with your healthcare provider before starting metformin. Since alcohol significantly lowers blood sugar, it may increase the risk of lactic acidosis as well as dangerous glucose imbalances.

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It’s also important to your healthcare provider if you’re prone to dehydration during exercise or for other reasons, as dehydration can increase your risk of lactic acidosis.

Warning signs of lactic acidosis include stomach pain, nausea, and/or vomiting; unusual muscle pain; drowsiness or fatigue; slow or irregular heartbeat; and trouble breathing. Seek immediate medical attention if you experience any of these symptoms.

Pregnant women can rest assured knowing that taking metformin during pregnancy is considered safe and, in fact, may help prevent complications. Research shows that women with PCOS also do better when they continue to take metformin during pregnancy.

In late September 2020, eight pharmaceutical companies voluntarily complied with a May 28, 2020 request by the U.S. Food and Drug Administration (FDA) to recall certain metformin products from the market. The FDA has previously found unacceptable levels of N-nitrosodimethylamine (NDMA) in some batches.

People taking metformin should continue to take the medication as prescribed until their health professional prescribes alternative treatment, if applicable. Stopping metformin in the absence of alternatives can pose serious health risks to people with type 2 diabetes.


Metformin is taken in doses ranging from 500 milligrams (mg) to 2550 mg per day. Your healthcare provider will start your prescription at a low dose and gradually increase it as your body needs. Depending on the form, take one to three times a day.

How to take and store

Metformin is an oral medication that can be taken as a tablet or liquid. Inhalation form is also available. Instructions must be followed to use each product safely. It can be safely stored at room temperature.

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Metformin should be taken with meals to prevent side effects. If you forget to take your medicine, take your next dose at your usual time, not double it. Seek medical attention if you accidentally take too much: It is important to stabilize your blood sugar right away to avoid serious health problems.

side effect

Metformin does not cause excessive hypoglycemia, which is an advantage over some other diabetes medications. It also does not cause weight gain and is beneficial for some cardiovascular risk factors. It may even help with weight loss and lower cholesterol.


Metformin can cause nausea, upset stomach, and diarrhea, especially when you first start taking it. It should always be taken with food to reduce the risk of gastrointestinal problems.

Over time, metformin may block the absorption of vitamin B12 in the body. Ask your healthcare provider if B12 vitamin supplements are right for you.


People with severe renal insufficiency or heart failure should not take metformin because in rare cases it can cause lactic acidosis. The risk is very low — about one in 30,000 people takes metformin — but the condition can be fatal.

Warning and Interaction

Although metformin is generally well-tolerated and has a good safety profile, you will need to work with your healthcare provider if you are combining this drug with other drugs such as insulin or sulfonylureas, especially Watch out for side effects like low blood sugar. When you combine metformin with other medicines, report any changes or unusual symptoms to your healthcare provider right away.

From diet to medication: treating type 2 diabetes