Metformin's protective effect on brain health emerges in 20-year study

A long-term follow-up of a clinical trial suggests that metformin, a common diabetes medication, may reduce the risk of dementia by about half. The effect was observed over more than two decades, though researchers caution that the result is not definitive. The exact biological reason for the potential benefit remains unknown.

The analysis drew on the Diabetes Prevention Program, a trial launched in the 1990s that enrolled 1,483 adults at elevated risk for type 2 diabetes. Participants received metformin, a lifestyle intervention combining low-fat diet with exercise, or a placebo. Cognitive assessments began in 2009, with a more intensive battery administered more than a decade later.

Earlier research has produced conflicting signals. Some studies linked metformin to higher dementia risk, possibly through vitamin B12 deficiency, while a 2022 meta-analysis pointed toward protection. A separate 2023 investigation involving over 210,000 diabetes patients found that longer metformin use corresponded with greater risk reduction, though the biological pathway remains unidentified.