"Using Observational Data from United States Electronic Health Records Alzheimer’s disease (AD)—the most common type of dementia—affects 5.7 million people in the US andcosts about $250 billion annually. Since there are no disease modifying therapies to date, repurposing FDA-approved drugs that reduce the risk of developing dementia offers an expedited path to reduce the impact of this epidemic. Here, we tested the hypothesis that metformin reduces the risk of dementia in diabetic patients by conducting an in-silico drug trial of metformin vs. another antidiabetic drug class, the sulfonylureas, in a real-world patient population of diabetics selected from the Research Patient Data Registry (RPDR), Boston-based Partners’ Healthcare Electronic Health Records (EHR) system. Using a causal inference framework, we found a significant effect of metformin compared to sulfonylureas on both risk and rate of onset for dementia as well as death."