The side effects I’m experiencing are mainly sinus congestion and fatigue (primarily the days I have the infusions). There are other side effects that people experience and it does affect your immune system. That’s the biggest concern for me!! Mesalamine worked for me for the couple months I was on it, until I developed drug induced pancreatitis. I was told to discontinue it immediately and within 13 days, started bleeding again and went into the worst flare I have ever had. Within weeks the diagnosis was “fulminant” and despite taking oral and rectal budesonide and then prednisone, the flare continued. The biologics were my last hope before surgery, so I reluctantly agreed to start the Entyvio. It was my last shot at something other than a colectomy. I was terrified and desperate, but it was all I had left to try... The doctors and the company that makes it (Takeda) are very clear about the many potential side effects and you are monitored closely at the infusion center at the hospital during each infusion. I’ve been on it since July and I am finally in remission. I’m cautiously optimistic that I will stay in remission and that I won’t have some of the really bad side effects that are possible while taking Entyvio. I also started a plant based diet a week before starting Entyvio and believe that is helping too. If I had been able to maintain remission on the mesalamine, I would not have started biologics. There are many more risks. If you’re in clinical remission on mesalamine, you may not have to advance to the next tier of treatment! I wish you luck and remission!!