For the treatment of obesity and diabetes, unimolecular peptides that target the glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors (GLP-1/GIP co-agonist) are now being tested in clinical settings [126,127]. Here, GCG is linked to obesity due to melanocortin 4 receptor deficiency.