Metformin (Met), a conventional drug for the treatment of diabetes, has been shown in numerous studies to be an effective HIF-1α inhibitor in cancer therapy, where it can reduce HIF-1α expression by up-regulating the p-AMPK pathway in cancer cells and inducing the expression of PHDS, which results in HIF-1α degradation by the proteasome. This evidence concerns the gene HIF1A and diabetes mellitus.