GIP and obesity due to melanocortin 4 receptor deficiency: It has been found that retatrutide, a 39 amino acid peptide, can resist cleavage by dipeptidyl peptidase IV, which is responsible for breaking down GLP-1 and GIP,271 and it also stimulates GLP-1, GIP and glucagon receptors, which is potentially useful for treating obesity and T2DM.