Sulfasalazine is used to treat a certain type of bowel disease called ulcerative colitis.This medication does not cure this condition, but it helps decrease symptoms such as fever, stomach pain, diarrhea, and rectal bleeding.fter an attack is treated, sulfasalazine is also used to increase the amount of time between attacks. This medication works by reducing irritation and swelling in the large intestines. In addition, delayed-release tablets of sulfasalazine are used to treat rheumatoid arthritis.