When I starting getting treated for Chrons my doctor, a Chrons expert, prescribed Pentasa. For the first couple of days it caused more abdominal pain and gave me temperature. This lasted for a somewhere between 2 - 4 days and then I was fine. I stopped taking it because it simply wasn't enough on its own and I needed stronger medication. I eventually was put on Remicade along with 6mp but still was having problems. My doctor added 8,000 grams of Pentasa a day into my treatment and approximately 3 months later I started feeling the best I had in years. Everyone reacts differently to these medications, but I hope hearing about my experience helps.