compositions and related methods for treating ibs and other gastrointestinal disorders and conditions , duodenogastric reflux , crohn &# 39 ; s disease , ulcerative colitis , inflammatory bowel disease , functional heartburn , dyspepsia , gastroparesis , chronic intestinal pseudo - obstruction , and disorders and conditions associated with constipation , e . g ., constipation associated with use of opiate pain killers , post - surgical constipation , and constipation associated with neuropathic disorders as well as other conditions and disorders are described . the compositions feature peptides that activate the guanylate cyclase c receptor .