My gut wasn't that bad when I got ME. I had a bit of Irritable bowel syndrome, but nothing awful. I don't think my gut was quite right but I 100% didn't have inflammatory bowel disease (IBD). I later had long term antibiotics for suspected Lyme and subsequently got ulcerative colitis, induced by the antibiotics. Stopping the antibiotics made the UC better very quickly but I was also put on mesalazine, a 5-aminosalicylic acid (5-ASA) drug which is used to lower inflammation. I later tried to lower the mesalazine dose from the maximum, but when I did I felt dreadful - my ME symptoms got a lot worse. As a result I've remained on the maximum dose. If I forget to take a dose, a few hours later I start feeling awful - again, I don't really think it's my UC getting worse, it's the inflammation I get with ME. It's not my gut that starts feeling bad, it's the muscles in my legs, loads more brain fog and confusion, and overall exhaustion, fatigue. I can pretty much feel inflammation rising in my blood. Although extra-intestinal manifestations of UC are unrecognized and it's likely I have some arthritis related to the UC, I'm sure that the mesalazine is working on my ME symptoms here, lowering whatever is driving it. It's possible that the source of this inflammation is the gut, but it's unlikely to be local and restricted to the colon because when I have forgotten a dose (which happens about once a month because I can't remember to take my tablets) upon realising I quickly take the forgotten dose and I start to feel better a couple of hours later. It's not possible that the tablets have reached my colon by then. The type of mesalazine I take is Pentasa which is a continuous release tablet and it starts to release in the small intestine. So either it's lowering inflammation there, it's getting absorbed into my blood then making it's way to the colon (in which case this could all be UC inflammation after all), or it's absorbed into my blood and lowering inflammation there or at some other location. Before I had UC I had some tests for inflammatory markers. Antibiotics lowered some of them, as they are known to do. But PGE2 didn't lower. It actually got higher on the treatment and stayed higher while I had colitis. I'm pretty sure the mesalazine is lowering this, and/or maybe some other type of inflammation that I've not had tested. Don't think there have been any studies of mesalazine in ME/CFS, which is a pity. The messlazine isn't a cure, I still have loads of inflammation but I guess it would be worse without it. I wish I knew for sure what it's lowering so I could find a more potent drug to take. Tagging @Dr.Shaqun as he's shown some interest in this topic. Edited story to make it shorter.