Proposed tissue targets of the major classes of anti-diabetes medications. For details, see Table 2. Although the primary tissue targets are shown, many of these drugs have multi-organ effects. The dotted line denotes putative mechanisms that remain to be fully demonstrated in humans. DPP-IV, dipeptidyl peptidase-IV; GI, gastrointestinal tract; GLP-1, glucagon-like peptide-1; TZDs, thiazolidinediones.