Common illnesses that may be confused with IBS include Lactose intolerance Drug-induced diarrhea Postcholecystectomy syndrome Laxative abuse Parasitic diseases (eg, giardiasis) Eosinophilic gastritis or enteritis Microscopic colitis Small intestinal bacterial overgrowth Celiac disease Bile acid diarrhea Early inflammatory bowel disease However, uninflamed colonic diverticula do not cause symptoms, and their presence should not be considered explanatory.