I was on sulfasalazine for many years very successfully, and my GIs have all said that research shows it's really the most effective drug (if a patient can tolerate it). I was on doses that ranged from 2,000 to 5,000 mgs per day. It especially helped with joint pain. It's dirt cheap.
I remember having some headaches when I started, but they went away within a week or two, especially as I started making sure to drink plenty of water. If I went anywhere sunny, I had to wear sunscreen and even then, I'd end up looking like a yam (as my friends put it). From time to time, my liver function tests were elevated and my platelets were low, but nothing serious.
I stopped taking it for a combination of reasons. I started having intense muscle fatigue, twitches, and some finger and toe pain. A neurologist thought it was the sulfasalazine. Those problems went away after I stopped the sulfa, but I also stopped calcium at that time. Too, the inflammatory arthritis moved into my spine, which is difficult to treat with any of the "regular" UC drugs, so I was left with opioid pain killers, biologics, or potentially, surgery. For now, I'm on Remicade.
I've tried different mesalamines, and they've always made things worse.