GCG and diabetes mellitus: Iridoids to regulate intestinal flora’s research are also insufficiently thorough, the active ingredient from iridoid monomers adjusts the perspective of intestinal flora, by adjusting the proportion of gram-negative bacteria, adjusting the lipopolysaccharide (LPS), short chain fatty acid (SCFAs), pancreatic glucagon like peptide 1 (glp-1) and so on protein content, absorb medications affect blood glucose metabolism, polysaccharide absorption metabolism, to iridoids for the further study of mechanism of diabetes, and pay attention to the connection between various mechanisms.