The main finding
In one sentence: Fifteen years after adults at high risk of diabetes were assigned to intensive lifestyle change, metformin or placebo, diabetes was 27% less likely in the lifestyle group and 18% less likely in the metformin group, although eye, kidney and nerve complications did not differ overall between the groups.
Group averages, not an individual prediction. A trial result describes what happened to a defined group over a defined time.
On this page
Why this study matters
Many Canadians are told they have prediabetes, a blood sugar level above normal but below the diabetes range. The Diabetes Prevention Program (DPP) was a landmark trial showing that lifestyle change or metformin could delay type 2 diabetes over three years. This follow-up asks two longer-term questions. Does the benefit last 15 years? And does preventing diabetes also prevent the small-vessel damage to eyes, kidneys and nerves that diabetes can cause?
Who was in the study
The original DPP ran from 1996 to 2001 and enrolled adults chosen to be at very high risk of developing diabetes. After it ended, 2,776 people, or 88% of the surviving group, joined the follow-up study, called the Diabetes Prevention Program Outcomes Study (DPPOS). It ran from September 1, 2002, to January 2, 2014. Average follow-up was 15 years counting from the start of the DPP.
What the researchers did
The DPP was a randomized trial. Randomized means chance decided which of three groups each person joined. The groups were an intensive lifestyle program, metformin (a diabetes medicine given as a masked tablet, meaning people did not know whether they had metformin or placebo), and placebo, which is an inactive tablet that looks the same.
At the end of the DPP, everyone was offered lifestyle training. During the follow-up, the original lifestyle group was offered reinforcement sessions twice a year. The metformin group kept taking metformin, now unmasked. People were analysed by their original group, an approach called intention to treat. The main outcomes were new diabetes and the presence of small-vessel complications, measured as a combined outcome of kidney, eye and nerve disease.
What they found
Over a mean of 15 years, diabetes was 27% less likely in the lifestyle group than in the placebo group, with a hazard ratio of 0.73 (95% confidence interval 0.65 to 0.83). In the metformin group it was 18% less likely, with a hazard ratio of 0.82 (0.72 to 0.93). A hazard ratio compares how fast an event happens in one group versus another. The confidence interval is the range within which the true value would likely fall. The differences between groups shrank over time.
| Result at year 15 | Lifestyle | Metformin | Placebo |
|---|---|---|---|
| People who had developed diabetes | 55% | 56% | 62% |
| Combined eye, kidney and nerve complications | 11.3% | 13.0% | 12.4% |
The complication rates were not significantly different between the groups (R32-C100). The confidence intervals were 10.1 to 12.7 for lifestyle, 11.7 to 14.5 for metformin and 11.1 to 13.8 for placebo.
In women (1,887 participants), the lifestyle group had a lower complication rate, 8.7%, compared with 11.0% for placebo and 11.2% for metformin. That is a 21% reduction compared with placebo and 22% compared with metformin. This was a subgroup result and needs cautious reading.
Across the whole study, people who did not develop diabetes had a 28% lower rate of complications than those who did (relative risk 0.72, 0.63 to 0.83). This is an observation, not a randomized comparison.
Side effects and people who stopped
The published summary we reviewed does not report side effects or how many people left each group during follow-up.
What this study does not tell you
- After the DPP ended, all three groups were offered lifestyle training. This likely narrowed the differences between groups.
- Preventing diabetes did not lead to fewer eye, kidney and nerve complications across the whole group. The benefit seen in women was a subgroup finding.
- The link between avoiding diabetes and having fewer complications is an association, not proof of cause.
- This study did not test any weight-loss medicine. It cannot be compared with medicine trials.
- The sponsor took part in the study design, conduct and publications.
What it means in Canada
This study supports the idea that lifestyle change can have a lasting effect on diabetes risk, though the effect narrowed over time and the trial did not show fewer complications overall. It does not involve weight-loss medicines. For information on medicines used in Canada, see semaglutide in Canada and tirzepatide in Canada. For coverage, see public drug coverage by province. To find diabetes prevention programs, see compare services.
Common questions
Did the Diabetes Prevention Program lifestyle change still work after 15 years?
Yes. Over a mean 15 years, diabetes was 27% less likely in the lifestyle group and 18% less likely in the metformin group than in the placebo group.
How many people developed diabetes by year 15 in the DPP?
Cumulative diabetes was 55% in the lifestyle group, 56% in the metformin group and 62% in the placebo group at year 15.
Did preventing diabetes in the DPP reduce eye, kidney and nerve damage?
Across the whole group, no. Rates of these complications were not significantly different between the three groups at the end of the study.
Related reading
Other studies in this library that bear on the same question.
Diabetes Prevention Program: lifestyle versus metformin
Diabetes Prevention Program: heart outcomes at 21 years
Look AHEAD eight-year weight loss results
Swedish Obese Subjects: surgery and diabetes prevention
Source
Original paper: Diabetes Prevention Program Research Group, DPPOS 15-year, The lancet. Diabetes & endocrinology, 2015. PubMed: https://pubmed.ncbi.nlm.nih.gov/26377054/. DOI: https://doi.org/10.1016/S2213-8587(15)00291-0. Funding: The study was funded by the National Institute of Diabetes and Digestive and Kidney Diseases, which took part in the steering committee, design, conduct and publications. How we summarized it: full text and extracted data.
This page explains a published study. It is not medical advice and does not describe whether a medicine is right for you. Talk to your doctor, nurse practitioner or pharmacist about your own situation. Reviewed and signed by two pharmacists registered in British Columbia, 2026-09-18.
Evidence records behind this page
Each record is a row in the clinical evidence file, taken from the published paper named above. The caution column is the limit the researcher recorded for that number.
This table scrolls sideways.
| Record | What the paper reports | Type | Population | Caution | Source |
|---|---|---|---|---|---|
| R32-C100 | At 15 years in DPPOS, cumulative diabetes incidence was 55% in the original lifestyle group,56% in the metformin group and 62% in the placebo group; overall aggregate microvascular outcomes did not differ significantly. | direct evidence | Original DPP adults at high diabetes risk | All arms later received lifestyle intervention; treatment differences attenuated. No overall microvascular advantage despite diabetes reduction. Primary 11832527, cardiovascular 35603600; corrected 10/21-year incidence reports excluded. | PubMed 26377054 |