Metformin for prediabetes: who it helps and how much

What prediabetes means

Prediabetes means your blood sugar is higher than normal but below the threshold for type 2 diabetes. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) defines it as an A1c of 5.7 to 6.4 percent, a fasting glucose of 100 to 125 mg/dL, or a two-hour glucose tolerance result of 140 to 199 mg/dL.

It is common. The CDC says more than 2 in 5 American adults have prediabetes, and it often goes unnoticed for years because it rarely causes symptoms. The U.S. Preventive Services Task Force recommends screening adults aged 35 to 70 who have overweight or obesity.

The trial that shaped the advice

The Diabetes Prevention Program (DPP), funded by the NIH, enrolled 3,234 adults with prediabetes at 27 U.S. centers. Participants were assigned to an intensive lifestyle program aiming for modest weight loss and regular activity, to metformin, or to a placebo.

Over about three years, lifestyle change reduced the risk of developing type 2 diabetes by 58 percent compared with placebo. Metformin reduced it by 31 percent. Both worked, but lifestyle change did more, and it worked across every subgroup studied.

Who benefited most from metformin

Metformin's effect was not evenly spread. According to NIDDK and the USPSTF summary of the trial, it worked best in:

• Adults aged 25 to 44, with less effect in people 60 and older
• People with a BMI of 35 or higher
• People with a fasting glucose of 110 mg/dL or higher
• Women with a history of gestational diabetes

What this means if you are 45 or older

If you are in midlife and leaner, the trial suggests metformin may do less for you than for a younger person with a higher BMI. Lifestyle change, on the other hand, was especially effective in older participants: NIDDK reports a 71 percent risk reduction in people aged 60 and older.

That does not rule metformin out. It means the decision depends on your numbers and risk factors, such as how quickly your A1c is rising, your weight, family history, and whether you had gestational diabetes or have polycystic ovary syndrome.

The long view

Participants were followed for many years afterward in the Diabetes Prevention Program Outcomes Study. At 15 years, NIDDK reports that metformin still delayed diabetes by 18 percent and lifestyle change by 27 percent compared with the original placebo group. Even so, more than half of people in every group eventually developed diabetes, which is a reminder that neither approach is a cure.

NIDDK describes metformin as a safe and effective generic medicine, and the study found it to be cost-saving over time.

How metformin works, briefly

Metformin lowers the amount of glucose your liver releases, improves how your body responds to insulin, and reduces glucose absorbed from food. It does not force the pancreas to release more insulin, so on its own it rarely causes low blood sugar. Weight loss with metformin tends to be modest; the USPSTF notes it modestly lowered weight in the DPP but did not consistently improve blood pressure or cholesterol.

Metformin compared with GLP-1 medicines

GLP-1 medicines such as semaglutide and tirzepatide produce much larger weight loss than metformin and are prescribed for weight management in people who meet the criteria. For someone whose main issue is excess weight, a clinician may discuss them instead. Metformin is older, inexpensive, taken by mouth and has decades of safety data, which keeps it relevant for many people with prediabetes.

Lifestyle change still comes first

The DPP lifestyle program aimed for about 7 percent weight loss and at least 150 minutes a week of moderate activity such as brisk walking. The CDC notes that losing 5 to 7 percent of body weight, about 10 to 14 pounds for a 200-pound person, can meaningfully lower risk, and that CDC-recognized lifestyle programs are available in many communities and online. Metformin works best as an addition to these habits, not a substitute for them.

Safety and monitoring

• Stomach upset is the most common side effect, usually early on; extended-release tablets often help
• Kidney function is checked before starting and periodically, as the FDA label restricts use at low eGFR
• Vitamin B12 can fall over time, so periodic checks are common
• The label carries a boxed warning for lactic acidosis, a rare but serious reaction; heavy alcohol use raises the risk
• A1c and fasting glucose are rechecked to see whether the plan is working

Metformin through HealifyMD

A licensed HealifyMD clinician reviews your labs, history and medicines and talks through lifestyle change, metformin and other options. If metformin fits, it costs $149 for 3 months ($50/month), confirmed at your eligibility review, with labs priced separately.