Metformin for Prediabetes: The Pros & Cons

Metformin is increasingly being prescribed for individuals with prediabetes to help prevent progression to type 2 diabetes.

This article explores the potential benefits and drawbacks of using metformin for prediabetes, including its effectiveness, safety, and suitability for long-term use.

What is metformin?

Metformin is sold under the brand names Fortamet, Glucophage, Glucophage XR, Glumetza, Riomet, and Riomet ER.

It is a prescription drug used to treat and manage diabetes by lowering blood sugar levels. It is taken orally as a pill and is in a class of drugs called biguanides. 

It is usually taken once or twice per day, most often with dinner. It is an extremely safe drug that is usually well-tolerated. 

Metformin works by lowering the amount of sugar produced by the liver, decreasing sugar absorption in the intestines, and improving insulin sensitivity, allowing individual cells in the body to consume more sugar and use that sugar more efficiently.

While metformin is not a magic pill, taking the medicine alongside adopting a healthier diet and increasing physical activity can lead to moderate weight loss, lower blood sugar levels, and improved HbA1c levels. 

Metformin is cheap and widely accessible in the United States. Most insurance plans, including Medicare, cover the drug. 

When should metformin be started for prediabetes?

In 2007, the American Diabetes Association (ADA) started recommending metformin as a treatment option for people with prediabetes to help prevent the onset of type 2 diabetes. 

Per the ADA, metformin “should be considered” for people with prediabetes, and especially for the following groups:

• Those with a BMI (body-mass index, a measure of weight relative to height) higher than 35 (classified as “moderate-risk obesity”) 
• People under 60
• Women with a previous history of gestational diabetes (a type of diabetes that occurs during pregnancy) 

However, it is not approved by the US Food and Drug Administration (FDA) for people with prediabetes.

Instead, many physicians prescribe the drug “off-label” to their patients with prediabetes to delay or even prevent the onset of type 2 diabetes. 

However, even with this off-label usage, fewer than 3 percent of adults with prediabetes currently use metformin. 

Because the medicine is prescribed for this condition in an off-label manner, there are no standard doses provided by manufacturers. Instead, your dose will be unique to you, based on your doctor’s guidance.

What are some of the pros of taking metformin for prediabetes? 

Taking metformin is a relatively low-risk intervention. If you have a physician who is willing to write you a prescription off-label, then taking the medicine may be worth a shot. 

It is generally well-tolerated, and people only usually have minor side effects (and usually just within the first few weeks of taking it, until their bodies adapt). 

As noted previously, it can help lower blood sugar and HbA1c levels, both of which, when high, are risk factors for developing type 2 diabetes. 

According to the Mayo Clinic, “You may notice an improvement in your blood glucose control in 1 to 2 weeks, but the full effect of blood glucose control may take up to 2 to 3 months.” 

A positive side effect of taking metformin, researchers are finding, is that it also may help protect against issues as varied as cancer, heart disease, obesity, neurodegenerative conditions, and vision problems. It may even act as an anti-aging supplement. 

Taken along with a balanced, nutritious diet and regular exercise, metformin can lead to weight loss, which can also help prevent type 2 diabetes. (That said, the weight loss is modest, so taking metformin alone as a weight-loss pill is not an effective strategy.)

Most importantly, taking metformin is effective in preventing or delaying type 2 diabetes in adults who are at high risk for the disease (with prediabetes being a risk factor). Taking the medicine daily has a comparable effect to implementing lifestyle interventions like an improved diet and exercise. 

What are the cons of taking metformin for prediabetes?

Taking metformin for prediabetes isn’t for everyone. 

For one thing, using metformin can cause uncomfortable side effects, including gastrointestinal issues like nausea, vomiting, and chronic diarrhea. These can be hard to manage, especially for people with rigid work schedules and social commitments. 

Additionally, if you are overweight or obese, metformin doesn’t guarantee weight loss. In one study, 29 percent of people lost 5 percent or more of their body weight, and just 8 percent lost around 10 percent. 

Additionally, people with severe kidney impairment or kidney disease will generally be directed to avoid taking metformin. Those with milder forms of kidney disease should have their kidney function monitored while taking the medicine if their doctors determine they are candidates for metformin therapy.

Another potential risk of taking metformin is that it can cause a decrease in vitamin B12 levels. Prolonged B12 deficiency can result in neurological problems, weakness, and fatigue. 

Metformin can also cause lactic acidosis, which is a serious and potentially deadly condition in which too much lactic acid builds up in the blood. 

The FDA requires metformin to have a “black box” warning about this dangerous side effect. 

Talk with your doctor before starting metformin therapy to see if taking this medicine is appropriate for you and your health goals. 

What are the side effects of metformin? 

The common side effects of metformin are (usually) mild, and include the following: 

• Nausea
• Stomach pain
• Cramping 
• Vomiting 
• Diarrhea 
• Loss of appetite
• Weight loss 
• Hypoglycemia (low blood sugar) if taken along with insulin