Key keywords: metformin, type 2 diabetes drug, 60-year old medication, unexpected brain benefits, cognitive decline reduction, Alzheimer's disease prevention, neuroprotective effect, drug repurposing First approved for clinical use to treat type 2 diabetes in 1963, metformin has remained the first-line oral medication for the condition for 60 years, prescribed to more than 150 million people worldwide each year. For decades, medical researchers only recognized its therapeutic effects on lowering blood glucose, reducing cardiovascular risk in diabetic patients, and minor benefits for weight management, with no documented links to central nervous system function. However, a new large-scale study published in *Nature Aging* led by a joint team from the University of Cambridge and the U.S. National Institutes of Health (NIH) has uncovered a long-overlooked, unexpected effect of the drug: it significantly slows cognitive decline and cuts the risk of developing Alzheimer's disease in high-risk groups. The research tracked 12,384 adults aged 55 and older with type 2 diabetes, split evenly between metformin users and patients taking other classes of diabetes medications, as well as a control group of 18,247 non-diabetic adults of the same age range, over a 10-year follow-up period. After adjusting for confounding factors including age, gender, baseline cognitive function, blood pressure, and socioeconomic status, the team found that metformin users experienced a 32% slower rate of cognitive decline compared to patients on other diabetes drugs, and a 21% lower risk of being diagnosed with Alzheimer's disease over the study period. Even pre-diabetic participants who took low-dose metformin as a preventive measure for diabetes showed a 19% lower risk of cognitive impairment than pre-diabetic people who did not take the drug. Further lab tests on mouse models and post-mortem human brain tissue revealed that metformin can cross the blood-brain barrier, reduce the accumulation of toxic beta-amyloid and tau proteins that are the hallmark of Alzheimer's disease, and reduce chronic inflammation in brain tissue to protect the function of neuronal mitochondria. Researchers noted that unlike new Alzheimer's drugs that cost tens of thousands of dollars per year and carry significant side effect risks, metformin has a 60-year track record of safety, costs less than $20 per month for most patients, and is widely available across nearly all countries. The team will launch a phase 3 clinical trial next year to test metformin as a dedicated preventive treatment for Alzheimer's disease in high-risk populations, with results expected as early as 2027. Medical officials emphasized that non-diabetic people should not take metformin without a doctor's prescription until the trial results are formally published and the indication is officially approved.