The invention provides a method of making a peptide comprising the amino acid sequence WDLYFEIVW (SEQ ID NO: 322) or a variant thereof, the method comprising (a) coupling the C-terminal amino acid of the peptide to a cleavable linking moiety bonded to a solid phase support material, wherein the alpha-amino group of the C-terminal amino acid that is to be coupled bears an Fmoc protecting group; (b) removing the Fmoc protecting group from the C-terminal amino acid that is coupled to the linking moiety; (c) successively coupling Fmoc-protected amino acids to the C-terminal amino acid, with attendant cleavage of the Fmoc protecting group prior to each successive amino acid addition, thereby producing an amino acid sequence bearing side chain protecting groups; and (d) removing the side chain protecting groups and cleaving the peptide from the solid phase support material.