How metformin works and why it's effective for type 2 diabetes
Metforminworks by decreasing the amount of sugar in your blood and increasing your body's response to insulin.
- Metformin is one of the most commonly used oral medications for people with type 2
diabetes, and it is very effective at lowering blood sugar and A1C levels.
- There are a few side effects of metformin, but these can be reduced by taking it with a meal.
- This article was reviewed by Jason R. McKnight, MD, MS, a family-medicine physician and clinical assistant professor at Texas A&M College of Medicine.
"Overall, metformin is a safe drug, and it reduces A1C up to 1.5% to 2.0%, which proves that it is very effective," says Dr. Anis Rehman, an assistant professor of clinical medicine in the division of endocrinology, diabetes, and metabolism at Southern Illinois University.
What is metformin?
Metformin is approved by the Food and Drug Administration for the treatment of type 2 diabetes, though it's sometimes used "off-label" to treat polycystic ovarian syndrome. The purpose of the medication is to lower blood-sugar levels.
Metformin lowers blood sugar in three ways:
- It decreases the amount of glucose, or sugar, that you absorb from your food.
- It decreases the amount of glucose produced in the liver.
- It increases your body's response to insulin, making you better able to use blood sugar for fuel, just as people without diabetes do.
Metformin is a prescription medication that comes in a liquid, pill, or extended-release tablet. It's usually taken two to three times a day with meals, though the extended-release tablet is taken only once a day. It is available as a generic drug or under a variety of brand names, including:
In addition, some combination tablets contain metformin along with other oral diabetes medications, such as glipizide or Pioglitazone. These combination medications include:
- Actoplus Met®
According to the American Diabetes Association, combination therapy can lower blood-sugar levels when metformin alone does not. People with initially high A1C levels of 7.5% to 9% may be advised to start combination therapy, though research is mixed on whether this lowers A1C levels faster than metformin alone.
How effective is metformin?
Metformin is very effective for most people with type 2 diabetes. In fact, a widely cited 2012 scientific review in Diabetes Care found that metformin reduced A1C levels by an average of 1.12% for patients with type 2 diabetes.
A more recent 2019 study published in the Pakistan Journal of Medical Sciences found that type 2 patients with the highest A1C levels saw the most dramatic increase after starting metformin.
The best way to measure the efficacy of metformin is to take an A1C test, which shows average blood-glucose levels over the past 12 weeks. As a result, you'll need to wait about three months after starting metformin to measure your A1C levels and get an accurate result, Rehman says.
Most people are prescribed metformin long term and should not stop the medication without talking to their doctor. "Diabetes type 2 is a chronic life-long disease, which means metformin is mostly prescribed for the long term," Rehman says.
It should be used along with lifestyle changes, like exercising more and counting carbohydrates, both of which can help control blood-sugar levels. In rare cases, in which patients effectively make major lifestyle changes, their doctor might wean them off metformin.
"In a small set of patients, with new diabetes type 2 diagnosis, lifestyle changes such as 10% body weight loss and carb-controlled diets can lead to diabetes type 2 remission," Rehman says.
Side effects of metformin
The most common side effects of metformin are gastrointestinal issues including diarrhea, flatulence, and nausea. As many as half of patients experience these, but they generally resolve in one to two weeks, Rehman says, and can be decreased by taking metformin with meals.
One serious but rare side effect of metformin is lactic acidosis, says Dr. Jordan Messler, a hospitalist at Morton Plant Hospitalist group in Clearwater, Florida.
Lactic acidosis occurs when lactic acid builds up in the body. This most commonly occurs in metformin patients when they are taking too much of the medication or also have kidney disease. Warning signs can include an elevated heart rate or respiratory rate, so contact your doctor immediately if you experience those.
Lactic acidosis occurs only about six times for the equivalent of every 100,000 years of patient use of the drug, however. "This is a rare event," Messler says.
During August 2020, two lots of extended-release metformin tablets were recalled because of contamination with the chemical N-nitrosodimethylamine. People on extended-release tablets should check with their doctor or pharmacist to see whether their pills were affected but should not stop taking them until they have replacement pills.
Overall, metformin is effective and has few side effects, which is why it has stood the test of time.
"Metformin has been in use as a treatment for type 2 diabetes since the 1950s," Messler said. "It has a strong safety profile, is well tolerated by patients, and has minimal interactions with other medications."
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