NPR3 and irritable bowel syndrome: IBS consists of four subtypes: IBS with constipation (IBS-C), IBS with diarrhea (IBS-D), IBS with mixed bowel habits (IBS-M), and IBS unclassified (IBS-U).9, –11 The IBS-C subtype comprises 26.3% of Chinese patients with IBS.12 Linaclotide is a guanylate cyclase-C (GC-C) agonist that has been approved to treat IBS-C in the United States, Europe, and China among others.