A 62-year-old woman presented to our hospital with watery diarrhea for 5 months since esomeprazole (EMZ) was first administered. On colonoscopy, linear ulcers and aphtha were noted in the sigmoid colon and cecum. Multiple biopsy specimens showed thickened collagen bands in the sub-epithelial layer. She was diagnosed with collagenous colitis (CC) . To dissolve doubts of EMZ-associated CC, she was administered famotidine. After 2 weeks, she showed an improvement in diarrhea. In Japan, the most common cause of drug-induced CC is lansoprazole. We report our experience with a case of EMZ-associated CC, which is rare in drug-induced CC.
