List of products in the National Drug Code with proprietary name . Olsalazine is used to treat a certain type of bowel disease called ulcerative colitis. It does not cure ulcerative colitis, but it may decrease symptoms such as stomach pain, diarrhea, and rectal bleeding caused by irritation/swelling of the colon/rectum. After an attack is treated, olsalazine is used to increase the amount of time between attacks. Olsalazine is a salicylate anti-inflammatory drug. It is believed to work by blocking the production of certain natural substances (e.g., prostaglandins) that may cause pain and swelling.