How Does Metformin Work?
Medically reviewed by Lindsay Cook, PharmD
To lessen the impact type 2 diabetes may have on your or a loved one's quality of life, you may turn to a prescription drug regimen to control high blood sugar (glucose) levels.
As such, your healthcare provider may recommend metformin, a prescription drug used to treat type 2 diabetes. It’s an oral medication that comes in several brand-name and generic versions. Metformin comes in immediate-release (IR) and extended-release (ER) forms.
Metformin is prescribed to manage high blood sugar levels in people with type 2 diabetes. Healthcare providers prescribe it alone or with other diabetes drugs. It’s typically the first medication a healthcare provider prescribes if they diagnose the condition.
Metformin acts through multiple mechanisms to control blood glucose. Specifically, it works by reducing the production of sugar by the liver. And it also decreases the absorption of sugar from your diet and boosts the body's sensitivity to insulin.
Keep reading this article to learn more about metformin, how it works, its side effects, dosage, and what to expect if your healthcare provider prescribes metformin.
Treating Diabetes
Type 2 diabetes is a chronic condition affecting the body's ability to metabolize sugar (glucose), leading to hyperglycemia (high levels of glucose in the blood).
Usually, when your blood glucose rises, the body releases the natural hormone insulin to help your body lower it. Insulin facilitates the movement of sugar into cells, where your body can process it into energy.
However, in people with type 2 diabetes, the body either doesn’t make enough insulin or has developed insulin resistance. This means your body is no longer sensitive or responsive to insulin release. As a result, your blood sugar levels increase.
Over time, high blood sugar causes damage to the body and can lead to severe complications, such as heart disease, vision loss, and kidney problems.
How Does Metformin Work?
The Food and Drug Administration (FDA) approves metformin to improve blood glucose levels in people with type 2 diabetes.
The drug is used in addition to diet and exercise in adults and children 10 and older with type 2 diabetes. Metformin belongs to the biguanide class of medications.
Metformin increases the amount of glucose taken in by your cells to produce energy. It works by increasing how well your cells respond to insulin.
Insulin is a hormone produced by your pancreas to regulate blood glucose levels. Insulin works by signaling your cells to increase glucose uptake from the blood. Once inside cells, glucose is used as a source of energy.
When cells take in more glucose, your blood sugar level decreases. In people with type 2 diabetes, the pancreas usually doesn’t produce enough insulin to meet the demand.
Glucose comes from the food that you eat and is used to produce energy. If you consume more glucose than your body needs for fueling your activities, the extra glucose is kept “in storage” in your liver as glycogen.
When the liver breaks down glycogen, it releases glucose into the body, increasing blood sugar levels. This leads to your body becoming less sensitive to insulin (known as insulin resistance).
Metformin works by increasing your body’s sensitivity to insulin. It also slows the breakdown of glycogen by the liver, thus lowering blood glucose levels.
When to Use Metformin
Metformin is a first-line treatment for people with type 2 diabetes. The American Diabetes Association (ADA) recommends metformin, and lifestyle changes, like diet and exercise, as the first intervention in treating type 2 diabetes.
Metformin is highly effective, safe, inexpensive and may reduce the risk of severe complications and death. Metformin is an oral medication conveniently easier to administer than injectable diabetes drugs.
This drug commonly causes stomach upset, such as loose bowel movements, especially when you start taking it. Gradual dose increases, and taking each dose with food helps to minimize these side effects.
It should not be used in people with specific health problems, including severe kidney impairment or metabolic acidosis.
Doing so increases the risk of a severe condition called lactic acidosis (a painful medical condition that can result in serious heart problems), including diabetic ketoacidosis.
Metformin is not used to treat type 1 diabetes. A healthcare provider can help determine if metformin might be suitable for you.
How Long Does Metformin Last?
Metformin IR takes about four days to get out of your system.
Comparatively, metformin ER provided greater blood glucose control and caused less digestive upset than IR metformin.
For context, ER medications gradually release a certain amount of the active drug over time, helping maintain more steady levels of the medicines in your body.
Regardless, the time metformin lasts in the body directly correlates with your specific diagnosis and dosage.
Side Effects & Safety
Metformin carries a boxed warning from the FDA cautioning against metformin use in instances of severe kidney impairment or metabolic acidosis.
Read below for specific side effects metformin has the potential to cause.
Common Side Effects
The most common side effects of metformin are digestive upset, such as diarrhea, nausea, vomiting, gas, and indigestion.
You can take metformin with a meal or snack to help lessen these side effects. Your healthcare provider will also start you with a low dose and increase it over a few days or weeks.
This approach also helps to minimize gastrointestinal (GI) side effects. Digestive side effects of metformin usually go away after a few days of consistent use.
Other possible side effects of metformin include muscle weakness, headache, and hypoglycemia (when blood sugar levels fall too low).
Severe Side Effects
Severe: Metformin carries a boxed warning for the risk of lactic acidosis. The risk of lactic acidosis is higher in people with severe kidney impairment.
Long-term: Though metformin is a relatively safe medication, using metformin long-term can affect vitamin B12 levels. Metformin can decrease the amount of B12 absorbed in the body.
Low vitamin B12 can lead to anemia and iron deficiency.
Your healthcare provider may monitor your B12 level using blood tests from time to time while you’re taking the medication.
You should not take metformin if you have the following:
Severe kidney impairment
A known allergy to metformin
Metabolic acidosis, including diabetic ketoacidosis
Be sure to discuss all of your medical conditions with your healthcare provider before starting metformin.
If you think metformin might be a good option, speak to a healthcare provider. Discuss your medical history, allergies, and all current medications, including prescription, over-the-counter (OTC) drugs, and supplements, with them. Sharing this information will help your healthcare provider determine if metformin is safe.
How to Take Metformin
You can take metformin exactly as prescribed by your healthcare provider. The following information describes typical or standard dosages.
The usual starting dosage of metformin IR tablets in adults is 500 milligrams (mg) to 850 mg, taken once or twice daily with food.
Your healthcare provider may gradually increase your dose over time. The maximum dosage is 2,000-2,250 mg per day. It is usually divided into three doses, one with each meal.
The usual starting dosage of metformin IR tablet in children is 500 mg, taken once or twice daily with food. The maximum dosage in children is 2,000 mg per day. This is usually divided into two or three doses with food throughout the day.
The usual starting dosage of metformin ER in adults is 500 mg, taken once daily with the evening meal. Your healthcare provider may gradually increase your dose over time. The maximum amount is 2,000 mg per day taken with the evening meal. You should not crush, cut, or chew metformin ER tablets.
Your healthcare provider may prescribe a lower metformin dosage depending on your kidney function. Also, you may have to pause taking metformin in preparation for specific medical procedures. A healthcare provider can tell you more about this.
Your healthcare provider will monitor your blood sugar and adjust your dose of metformin accordingly. You can also check your blood sugar levels at home.
In many cases, metformin may not be enough to bring your blood sugar levels within your goal range. Your healthcare provider may prescribe additional diabetes medications to help control your blood sugar.
Metformin Interactions
Interactions may occur with metformin. Some drug interactions can be dangerous, while others are unlikely to have consequences.
Your healthcare provider can help you avoid or manage interactions. Before taking metformin, talk with your provider about all your current medications, including OTC and supplements.
Interactions with metformin may include:
Carbonic anhydrase inhibitors: Carbonic anhydrase inhibitors (CAIs, a category of diuretics), such as acetazolamide, methazolamide, Topamax (topiramate), Zonisade (zonisamide), and Cosopt (dorzolamide), may increase the risk of lactic acidosis
Certain drugs can increase metformin levels: Certain medications may cause metformin to build up in the body, increasing the risk of severe side effects. Examples of drugs that could lead to a build-up of metformin if taken together include Asprzuzyo Sprinkle (ranolazine), Tivicay (dolutegravir), and Tagamet HB (cimetidine).
Other diabetes drugs: Sometimes, medicines used to treat diabetes can cause blood sugar levels to drop too low. If your healthcare provider prescribes additional diabetes medications, they may recommend frequent blood sugar checks. Or they may lower your dose of metformin.
In addition, consuming alcohol while taking metformin can increase your chances of developing a serious condition called lactic acidosis by increasing the amount of lactate in your body.
Before starting metformin, talk to your healthcare provider to determine if you should avoid or limit alcohol use while taking this medication.
Summary
Metformin is an effective and commonly administered drug for treating type 2 diabetes.
Metformin works by decreasing the amount of glucose in your blood, slowing glucose production in the liver, and making your body more responsive to insulin so your cells can better utilize glucose as energy.
Metformin commonly causes stomach upset at first. This can be minimized by taking the medication with food, which typically eases within a few days.
Talk to a healthcare provider if you have questions about taking metformin.
Frequently Asked Questions
Can lifestyle changes help my diabetes?
Yes. Diet and exercise changes can tremendously impact diabetes and your overall health.
Studies have shown an association between weight loss from healthy lifestyle changes and remission of type 2 diabetes—potentially reversing the condition.
The ADA recommends that people with diabetes get at least 150 minutes of moderate-intensity exercise weekly.
What are common brand-name alternatives that contain metformin?
The original brand name of metformin was Glucophage, but it was discontinued. Available brand versions of metformin include Glucophage, Glumetza, Fortamet, and Riomet.
Metformin is also an active ingredient in many combination drugs for diabetes. Combination drugs offer the convenience of two medications in one pill. Examples include: Actoplus Met (metformin and pioglitazone), Invokamet (metformin and canagliflozin), Segluroment (metformin and ertugliflozin), and Synjardy (metformin and empagliflozin).
