Statins can be effective at lowering cholesterol, but they have a perplexing tendency to work for some people and not others. Gut bacteria may be the reason. A research team led by a Duke University scientist has identified three bile acids produced by gut bacteria that were evident in people who responded well to a common cholesterol-lowering drug called simvastatin. The finding, published Oct. 13, 2011, in PLoS One, demonstrates how gut bacteria can cause inherent differences in the way people digest, metabolize and benefit from substances such as drugs.