Ulcerative colitis (UC) is a chronic inflammatory bowel disease, which typically presents with faecal urgency, diarrhoea (frequently occurring at night and after meals), blood and mucus in stool, and abdominal pain. Initially, UC involves the rectum and spreads proximally in a pattern to involve all or part of the colon. Features of UC are dependent upon the extent, as well as the activity, of the disease, which can be severe, moderate, mild or fulminant. There is no medical cure. Firstline therapy for patients with mild−to−moderate UC is the use of compounds containing 5-aminosalicylic acid (5−ASA). Asacol is a modified−release formula of mesalazine designed to release 5−ASA at a specific pH in the gut.