Compositions and methods are disclosed for the treatment of diabetes and related diseases using peptides with incretin hormone activity. Preferably, the peptide with incretin hormone activity is GLP-1, exendin or an analog of GLP-1 or exendin. The peptides with incretin hormone activity are administered transepithelially using a transepithelial carrier peptide. The transepithelial peptide contains sufficient amino, guanidine or amidino groups to stimulate transepithelial delivery. In some embodiments, the transepithelial carrier and the peptide with incretin hormone activity are embedded in a pressure sensitive adhesive layer of a plaster or patch.