Study participants were randomized to one of three groups: treatment with metformin, intensive lifestyle intervention, or placebo. Randomization to placebo and metformin was double-blinded.
Subjects assigned to the metformin arm received 850 mg a day for 1 month, which was titrated to 850 mg bid thereafter. Those assigned to lifestyle intervention were expected to engage in moderate exercise (eg, brisk walking) for at least 150 minutes a week and to achieve and maintain a weight loss of at least 7%.
A 16-lesson curriculum that covered diet, exercise, and behavior modification was taught by case managers on a 1-to-1 basis during the first 24 weeks after study enrollment.
The average follow-up was 2.8 years with a range of 1.8 to 4.6 years.

Diabetes Prevention Program Research Group. N Engl J Med. 2002;346:393-403.