GCGR and obesity due to melanocortin 4 receptor deficiency: <h4>Background and hypothesis</h4>Retatrutide is an agonist of the glucose-dependent insulinotropic polypeptide, glucagon-like peptide-1 and glucagon receptors that reduced weight and hemoglobin A1c (HbA1c) in individuals with obesity and type 2 diabetes (T2D).