Cochrane for Clinicians

Putting Evidence into Practice

Metformin to Prevent Diabetes in Patients at Increased Risk


Am Fam Physician. 2020 Nov 1;102(9):531-532.

Author disclosure: No relevant financial affiliations.

Clinical Question

In patients at increased risk of developing type 2 diabetes mellitus, is metformin effective for the prevention or delay of diabetes onset and its associated complications?

Evidence-Based Answer

In patients at increased risk of developing type 2 diabetes, metformin reduces the risk (number needed to treat [NNT] = 7; 95% CI, 6 to 10) compared with counseling on standard diet and exercise. Data are limited regarding adverse effects and long-term outcomes.1 (Strength of Recommendation: B, based on inconsistent or limited-quality patient-oriented evidence.)

Practice Pointers

Patients with prediabetes, defined as impaired fasting glucose, impaired glucose tolerance, and/or an A1C of 5.7% to 6.4%, are at increased risk of developing type 2 diabetes. Type 2 diabetes has been associated with many complications, including neuropathy, retinopathy, cardiovascular disease, and kidney dysfunction.1 According to the Centers for Disease Control and Prevention, 13% of the U.S. population 18 years and older were diagnosed with type 2 diabetes in 2018.2 From 2013 to 2016, 34.5% of the U.S. population 18 years and older were diagnosed with prediabetes2; 15% to 30% of these patients progress to type 2 diabetes within five years.3

The authors of this Cochrane review investigated whether metformin reduces the risk of type 2 diabetes in patients with prediabetes.1 The review included 20 randomized controlled trials and 6,774 patients. The duration of intervention ranged from one to five years. The authors included trials that compared metformin with any pharmacologic intervention, behavioral intervention, placebo, or standard of care in populations with prediabetes. The primary outcomes of interest were all-cause mortality, incidence of type 2 diabetes, serious adverse effects, cardiovascular mortality, nonfatal myocardial infarction or stroke, health-related quality of life, and socioeconomic effects.

Patients who used metformin for one to five years were less likely to develop

Author disclosure: No relevant financial affiliations.


show all references

1. Madsen KS, Chi Y, Metzendorf MI, et al. Metformin for prevention or delay of type 2 diabetes mellitus and its associated complications in persons at increased risk for the development of type 2 diabetes mellitus. Cochrane Database Syst Rev. 2019;(12):CD008558....

2. Centers for Disease Control and Prevention. National Diabetes Statistics Report, 2020. Accessed October 2, 2020.

3. Centers for Disease Control and Prevention. Prediabetes: could it be you? 2014. Accessed February 14, 2020.

4. Barry E, Roberts S, Oke J, et al. Efficacy and effectiveness of screen and treat policies in prevention of type 2 diabetes: systematic review and meta-analysis of screening tests and interventions. BMJ. 2017;356:i6538.

5. National Institute for Health and Care Excellence. Type 2 diabetes: prevention in people at high risk. Public health guideline [PH38]. Updated September 15, 2017. Accessed February 14, 2020.

6. American Diabetes Association. 5. Prevention or delay of type 2 diabetes: Standards of Medical Care in Diabetes–2018. Diabetes Care. 2018;41(suppl 1):S51–S54.

These are summaries of reviews from the Cochrane Library.

This series is coordinated by Corey D. Fogleman, MD, assistant medical editor.

A collection of Cochrane for Clinicians published in AFP is available at



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