Mesalamine is used to treat ulcerative colitis (a condition which causes swelling and sores in the lining of the colon [large intestine] and rectum) and also to maintain improvement of ulcerative colitis symptoms. In clinical trials of active ulcerative colitis comparing mesalamine with placebo, the fraction of patients with adverse events ranged from 13% to 73% with mesalamine vs. 22% to 61% with placebo (Loftus et al 2003). The most commonly reported adverse events with the 5-ASA formulations include headache, GI symptoms such as diarrhea, bloating, nausea. Other rare side effects include interstitial. Mesalamine may cause an acute intolerance syndrome that resembles a flare of inflammatory bowel disease (Crohn's disease or ulcerative colitis) with cramping, abdominal pain, and bloody diarrhea. Fever , headache , itching , and rash also may occur. Summary. Diarrhea is found among people who take Mesalamine, especially for people who are female, 60+ old , have been taking the drug for 1 month, also take medication Humira, and have Pain. Canadian to get early space flight mesalamine diarrhea after Soyuz investigation. See Full Story Correspondence from The New England Journal of Medicine — Diarrhea Associated with Mesalamine in a Patient with Chronic Nongranulomatous Enterocolitis Mesalamine has been used as the first-line therapy for the treatment of ulcerative colitis (UC) because of its efficacy and fewer side effects. However, earlier study showed that mesalamine occasionally causes diarrhea. We are presenting a patient with active UC in whom bloody diarrhea accompanied Mesalamine gives me ferocious D, whether I take it orally or rectally. But that's not the usual reaction, so it could really be either. You might try either stopping the mesalaming or going back on the entcort for a bit to see if it changes anything. Mesalamine affects a substance in the body that causes inflammation, tissue damage, and diarrhea. Mesalamine is used to treat mild to moderate ulcerative colitis. Prescribed mesalamine for ulcerative colitis in Jan this year after two weeks had severe tummy cramps, bloody diarrhea, headaches, fevers, nausea and rashes.