Summary Drosophila can be used to discover the underlying molecular mechanisms by which metformin effects lifespan. From 112 tested cohorts, we found metformin can extend fly lifespan as much as 30% but in other conditions the compound equally reduced lifespan. Here we propose to identify genetic factors that contribute to this variation. We will conduct a genome wide association (GWA) analysis with Drosophila, combined with emerging bioinformatic analytics and molecular validation studies. We propose as well, an innovative approach to bridge Drosophila analysis to humans and mice by mapping response SNPs of the fly onto orthologous gene expression data from mammals. We will combine these approaches to resolve how metformin affects aging, and through which pathways it positively or negatively modulates lifespan.