I work in contract research and my work life revolves around drug development. I should state that I think people should life the healthiest lifestyle that they can and avoid all drugs, if possible. That being said, people will sometimes need drugs for a number of reasons.

I've always thought Metformin was one of the better drugs - it's cheap and helps diabetics get glucose control, eventually allowing the more motivated patients to make lifestyle changes and wean off the drug.

Here is an in vitro study from 2009 showing that Metformin increased Alzheimer amyloid peptides.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2656178/

Metformin is helping in the area of glucose control, but might be allowing the diabetic patient to still over consume food, causing damage in areas of the brain - perhaps giving some credibility to concept of Alzheimer is diabetes of the brain.

I think the take-away from this study is to get glucose control and try to get off as many lifestyle medications as possible, with your doctor's help. When we take drugs that artificially improve our test results (cholesterol, trigs, glucose), there might be unintended consequences that have not yet been fully realized by the research community.